I feel this is something Aleph One desperately needs. Mouse control is the major thing that puts newcomers off.
I know part of it has to do with film compatibility, but I honestly don't see the issue. Old demos could still play back fine, and new demos could be recorded with a new input system.
I suggest having a significantly higher resolution angle/pitch measurement (at least 16x, so 4 more bits), and removing the speed caps. I know the engine itself only handles 512 degrees IIRC, so the hi-res stuff could be rounded for internal use. Other than that, have the hi-res affect camera angle/pitch, but not the gamesim.
I imagine that speed cap removal would be less of an issue, since you could just set the angle/pitch to whatever at any tick, as opposed to writing in new angle/pitch handling on the gamesim.
______
Alternately, I suggest a "virtual mouse" that drives the original protocol. Basically, the user drives a "target point" that the "virtual mouse" driver drives the original protocol to try going to that (converted) target position as quickly as possible.
This may be a less intensive solution.