Dairwolf,
I actually love discussions like this, much to the shegrin of some teachers and friends I know who don't like the notion of "thinking" our way out of these log jams. I inwardly counter that as humans, it *IS* our ability to THINK that enables even those of us without some natural gift a shot at making things better.
I think I see what you're getting at, and the truth of course is that whether or not it works for you is a '"time will tell" thing. Anything like this that seems to feel good and makes sense, you have to give a good month or so just to see whether it truly works. I'm sure you'd agree its a safe bet you (a) will go through MANY more cycles of refining this thinking while adding/subtracting different moves, and (b) occasionally getting a bit frustrated at the whole process and backing away.
I will add this to the pile of confusion/solutions, especially the part about how different it would be were there only one string to worry about. Over the past year, amid much online exploration and some help from online instructors, I've looked carefully at everything I do on the guitar, particularly the right hand work. I've continuously looked and watched to honestly see and hear what works, what could work better, what doesn't work, and what I could do differently about the things that don't. As you can imagine, and are seeing yourself, its that last part that often seems endless.
Now over time some of the problems I'm successfully solving (but by no means have FINISHED) include things like making my picking on lower strings as fluid as picking on the upper ones, and improving my control and alt picking. Some of the specific things I've done along the way include keeping my picking angle constant (by moving my arm/wrist when its time for a string change), and distributing the job of picking over more muscle groups, targeting some weak muscles I inwardly believed were being underused., and picking lighter and constantly without "digging in". Of course the the whole issue of changing strings is important, but on honest assessment I was shocked at how much ground work I needed to do first, just to continuously play any individual note on any string at any tempo in a relaxed and consistent manner. Funny how the obvious can elude my brain for so long.
But having gained some good ground improving the basics, the first thing I've worked on in the "changing strings" category was to make my "outside" ALT picking as fluid as my "inside" alt picking. As I mentioned, when I discovered that unlike 90% of other guitarists I had always found "inside" picking easier, that made me realize that technically they are both identical mirror images of each other, so it HAD to be POSSIBLE for me to equalize them. I honestly have to say that this was a true case where a lot of my friends were right. If Inside and outside picking both have the same "problem", and are just the reverse of each other, then clearly I had to start by substituting simple "BELIEF" for some of my thinking. You wouldn't believe to what lengths I had gone to avoid "outside" alt picking! I had actually re-arranged all my scales to have an even number of notes on any given string, just so i would never have to reverse. Well that turned out to be a good left hand exercise, but it was as if i just abandoned the idea of actually fixing the problem. And perhaps it WAS a problem for some unknown reason at one time, but over the past year I seem to have mostly fixed it so that they are now equally easy (or equally difficult depending on whether I'm having a good or bad day).
Now in doing this, and I don't know if its helpful or not, a couple of things I've done have seemed to be winners. First, I mentioned I'm trying to concentrate on using my arm when its time to change strings, mostly to keep my picking angel constant. I've also been trying to use my thumb and first finger to do some of the pick motion, mostly to conserve wrist motion and pick lighter (less energy means more speed and less fatigue). And finally, I've added an exercise I got from an online teacher, which is that when I play a scale (this is at lower tempos), I make long wide motions with the pick after each note. The teachers original intent was to reduce tension, which it does. But just as important, there is no way you can make a big motion without hitting the next string unless you make each pick move in a slight upward direction, as you already acknowledged. The result of that, even on one string, is a kind of "figure 8" motion of the pick in 3 dimensions if you analyzed it with a camera. That motion, which makes you avoid the next string in your wide motion, is also teaching your hand to alliterate pick! Further, its probably not the kind of thing you could think about at higher tempos, but it is the kind of thing that your hand just gets used to doing. The specifics of whether you should move your hand off to the side as you do this, or which muscles are actually doing the work is a hard matter to nail down, because you can do a a million things in a way that is wrong for you at the slow tempos needed to learn new moves. One thing I do (which at least one teacher also mentioned so that my thinking was confirmed) is this. When I'm at my best and playing my fastest (the days the wind is blowing the right way I guess), its good to look at yourself in a mirror and see what you're doing. Sometimes the motions you already make when you're playing fast (even if its something simple) are valuable to try to apply to your slower practice work.
And slow remains a huge key to playing fast! At least for me all this has meant that whatever else I'm practicing, I need to spend time working slow enough that I can keep all these motions and corrections in mind. Its literally meant being willing to start over, in order to learn to be a better player this time. I've been playing 40 years so that's saying a lot, but I'd encourage you... taking things apart this way has given me more improvement in the past year (at least technically) than in the last 15 combined!. And yes, there is still the chance of setbacks, that some motion essential to YOUR playing may get overlooked. But if you keep at it, and make sure you try everything for at least a month to see if its making any difference at all, you will make progress here! Work slow at these moves you're learning and trying. Remember, working slow on the metronome doesn't mean you actually pick or move slow. You're still practicing each move as a sudden motion, as if you were playing insanely fast.... but there's just more time in between each move. Time to absorb what you just did.
Now just sharing here, MY next personal dilemma/project at the moment is not so much changing strings when there are multiple notes on each string. that still needs work but is coming along fine. My big hitch is what to do when there is an arpeggio involved that requires you to either alt-pick your way across the neck, suddenly switch from alt picking to a sweep, or (again) re-arranging all my arpeggios so they can be done with long left hand reaches that avoids having to play one note per string across several notes. This subject is one I've seen discussed and argued more than any other!!To *ME* it seems that if your alt picking your way up a scale and then suddenly need to come down 3 or 4 notes on as many strings (an arpeggio, usually), then a sweep would be most efficient, and has the best chance of "keeping up" with what I can do on just 1 string. But there seems to be some serious mental block going on to making it work, and I haven't figured out yet. Consider the seemingly simple move of picking a 4th interval between two strings, lets say a "B" note on the 5th string and an "E" note on the 4th, in such a way that you hit each note twice. You'd think it would be hugely easy to just play B-E in one direction, and then reverse and pick E-B in the other (B-B-E-E-B-B-E-E etc).. From a motion point of view that sure seems to be both ideal and easy. In practice, not so much. Stay tuned!