You make some good points. However, I disagree with a few things. I don't think that the custom textures thing is an issue, because people will mostly find this game through steam, and, even if the game did get a mature rating, it would still be easy for young players to play it. If a game is rated mature and it is on Steam, it just means you have to enter your birthday to visit the store page. This happens no matter what you Steam account birthday is, and getting around it is as easy as saying your birthday was the 1st of January 2000. I honestly doubt the game would get a mature rating due to this, and, even if it did, it would not cut off any of the player base.
I can see why you think more matchmaking would be good, but I don't believe it would work in the long term. This game will always be niche, and I think that, after the initial release, there won't be enough players left for matchmaking to work. People will become frustrated with the long waiting times, and quit the game. At least with the current system they can watch other people fight and they know when they will be able to play.
I think the best solution is to keep the room system, but have multiple fights going on at the same time. This would be the default system, but there would be an option to change the server to the queue mode we have now, so that bet servers still work.
I agree that the menu needs to change, though. Free play should not be the largest and first option.