Excuse me? I hope you're kidding.. If not, then: If you can't play more than 6 or 7 strings, it doesn't mean that 8 or 9 is useless and stupid.
It is not about playability (which is not as good as the fretboard becomes to wide), it is also harmonic facts:
a 7th low string closes the gap to the base player.
a 7string downtuned is already many times at least 1 string in the bass players range.
8 strings = you could reason with me that this is slightly usefull as it would make it less important to downtune the other strings (keep the guitar in standard tuning) while skipping in parts that usually the bass should play, but you want distorted
9 string: you are way in the bassplayers region (I guess some might even downtune that lol) and harmonic progression from the high E (if you did not downtune) to the lowest string in a scale that is not overloaded or I would not like to open my veines for when hearing it is not likely.
also you could argue special needs (higher strings, or two strings with same tuning etc.), however the people I know that could make use of such an instrument are so rare, that most of those players already own such special weapons, custom made. I cannot envision a mass produced modell for this. (you can get such beasts from basslab for example)
but hey: I am always open minded. if you buy one and post a video giving a demonstration what this beast is for (mass produced), let me know and I might make up my mind.
And I sure hope before you post such a thing, that you can make use of those strings. As I have seen several people with 7s and about 30% of the people I have seen play 7s really make use of that guitar in a reasonable way, as many do not understand how scales expand over the new string. Many just use it because they do not want to switch downtuned guitars between songs and many of those folk actually would need a 3 string powermush guitar. (No idea if they play actual powerchords as most of the time you cannot hear which chord they play anyways.)