It's not so much a question of if it's possible, it surely is, but rather a question of ease of execution, something which I think OP hasn't really considered.
I'm somewhat new to Osu! so I don't remember when catch the beat or Taiko were added but transposition of taiko maps is just taking the timing and if there's a different beatsound for the rim hits, CTB is, more or less, just taking the X position of the beatmap to make the fruit.
Osu!Mania obviously came much later but it was pretty similar I imagine, timing and sliders transpose well.
With Touhosu! however, things are a lot less clear, and the relationship with any real sense of timing is tenuous at best. The original beatmap can be an x,y co-ordinate for bullet spawn points and timings. But how do you make that into genuinely interesting gameplay?
The video by Evast is impressive in a lot of ways and rather than getting bogged down in the challenges I will use that as a basis for my suggestions.
First of all, I think there needs to be an acceptance that on higher difficulties the bullets will make impossible to dodge patterns and some sort of bombing system is needed. Highly strategic bomb use becomes part of the strategy and means that the possibility of more difficult patterns is opened up. CTB had maps that couldn't be full combo'd for a while before the superjumps were introduced. Find a way to make the difficulty doable, rather than shying away from the difficulty in the first place.
This frees up more interesting bullet types to be used. Like Keine's lasers from IN stage 3, or the homing-streaming bullets of stage 5 of PCB. At presemt Evast uses 2 bullet types it seems. If the type of bullet spawned changes with combo and there was a wide variety of bullets, particularly bullets that react to the way the player is moving (when they are fired, no properly homing bullets of course). At present the bullets just move out from their spawn point in a fixed way regardless of what the player does. ZUN uses bullets in a way that zones you around the level by aiming near you with streams. You feel involved rather than like you're dodging a pre-established pattern.
And maybe have a ball that moves around the far end of the level you can shoot at for bonus points meaning players who control their movement more get more points.
But again, this is so monumentally more difficult than implementing any of the other game modes so far because it's about making a dynamic system that has an interesting result with far less control over what the player actually has to do.
I would be quite pleased if happens, don't get me wrong, I just think that the whole request is somewhat of a trap. Seems like a great idea and is thus not instantly dismissed, but is intensely difficult to implement. It seems like the kind of thing that could be an absolute time sink and produce poor results for the time invested and that OP surely didn't think things through enough when they requested this.
yeah but don't tell anyone