This is just a fun idea I've had for a while. I think a multiplayer Touhou patch/fangame might actually be pretty fun, albeit chaotic. Here's how it would work, in my eyes:
Each player would have to pick a different shot type/character, depending on the game. In games like UFO and DDC, each shot type would count as a different character. That way, everyone won't just pick the character with the longest invincibility time during their bomb and spam the heck out of it. Also, imagine all the petty arguments over who gets what character! Hilarious. Because of this, the max players would be 4, because of EoSD, and also because any more would clog the screen. Everyone would have separate life counters, but whenever someone got an extend, it would be shared with everyone. In games with life pieces, everyone gets one whenever one is picked up. This works like a Mario game, so that even people who lose all their lives can come back if someone else manages to carry them. (This would be a pretty casual experience, considering how easy it would be to 1CC games.) Everyone has separate power, so that one person dying wouldn't weaken everyone. This means that people need separate bomb counters, too, because of how MoF and SA work. However, I think it would be fair to not share bombs across every player. This makes picking up power and bombs/bomb pieces somewhat strategic. Do you give it to the weakest player, or the one who can use them most effectively? Also, if there are two people, then everyone does half damage. If there are three, a third the usual damage, and so on, so you don't murder everything instantly. I don't know how Score would work, but there could probably be some kind of "score battle" mode where you compete to gain the most score in a run or a stage.
So, yeah. It would mostly just be chaotic fun with friends, like MarioKart or the like. I don't actually have the capability to do this- I only started learning Danmakufu like two weeks ago- and I doubt it will become a reality, but I think it's a cool concept. That's why I put it here instead of in RaNGE.
Also then maybe I could get my friends to play Touhou
EDIT: Now that I think about it, Power should work the same way lives do- everyone has a separate counter but getting one piece gives it simultaneously to everyone. If whoever picked up the piece was the only one who got it, it would just be a fight over who can stay in the POC the longest, and characters like Marisa (from any game, between the guaranteed POC in every game and lowest POC line) and SA!ReimuB would be broken as hell. This would make it easy to just bombspam MoF and SA, but there's probably a fix for that, and hey this was always going to be broken anyway.