Protocol was bad a$$! I'm glad I got to see them. Holdsworth played here about when our second kid was born and I missed that but I wasn't about to miss Greg Howe. And Simon Philips? Amazing! I started doing my own instrumental tunes really after hearing Jeff Beck - long after being exposed to Satch and Vai. And with records like "There and Back" Simon Philips is very much a part of that audio DNA. Amazing drummer live! My wife, who I will say is WAY more into mainstream stuff, liked it too.
Not to derail further but: Greg looked like he struggled a bit with his guitar the first couple of songs but he eventually fell right in I think. Simon dropped a stick on the opener and didn't miss a beat. He could probably drop a bag of sticks while playing odd meter and not get lost for a second. Incredible!
Getting back on topic, to me mainstream in rock is who the twenty somethings are going to see at a festival show. Maybe it's Paramore. Maybe it's Cage the Elephant. Maybe it's Red Hot Chili Peppers if they release a new record everyone likes. Maybe it's Weezer. And all those bands have an internet presence too. Sure, I dig Vai and Satch more but to argue they're mainstream or anything close to it is just not the case IMO.
But, as with Greg Howe and Protocol, the niche fanbase can get a big surge of energy from the internet. The first crowd funded thing I ever donated to is Paul Gilbert's new record. Also, I was born in the early seventies so I would have never known how awesome 70's rock is if it weren't for the internet. I always thought Thin Lizzy or ZZ Top were just okay from the stuff they played on the radio but with online streaming I listen to their catalog over and over again avidly.
I also really dig R&B soul. The Isley Brothers, The Time, Prince, The Gap Band, Stevie Wonder, The Ohio Players, Parliament, The Brothers Johnson... some of these acts are no longer mainstream R&B either they way DLR is no longer mainstream rock. Thank God for the internet allowing us access to so many of their recordings. (Also, if you haven't heard Jessie Johnson or Ernie Isley play guitar you really should do yourself a favor and listen to some of the records they're on.)
And now that (you're right) there isn't really the big influence of radio I like to try and find new acts; so I don't think of myself as the curmudgeon stuck in his childhood genre of music.
That's how I found Hard-Fi, Interpol, The Killers (who get radio play), and Mastodon (who are amazing!).
Ok, long rant but I'll end with this. It is fun to see someone who was "niche" gain more of a mainstream appeal. And that name is Richie Kotzen. I remember picking up Richie's early Shrapnel stuff and then when "Fever Dream" it I was all "WTF?!?" But I DUG it! I think Richie did more to introduce me to R&B than probably any other act. And it's good to see him get more mainstream respect. I knew it was possible for him to get there way back at "Mother Head's Family Reunion." Now is his current success "mainstream?" Maybe. But it's closer now than it was in 1994. Good on him!