The thing with a FPS RPG is that you get the Morrowind Syndrome: a first person game, but your actions are governed by dicerolls.
I don't think a lot of people would like that, even if I personally like it in Morrowind. Though, with the right features (like proper animations that simulate dodging, parrying, critical misses, and so on) it would be very interesting. You know, dice rolls, but dice rolls you can't tell are clearly happening (like Morrowind's in-your-face misses).
I've played JSawyer before, and augmented it with a few more mods for a more hardcore game, if only because I wasn't quite seeing the RPG in FPS, so I went with the logical approach: if you can't make a correct RPG out of a FPS, then go full FPS (lethal bullets, slow stimpak healing, Guns skill only affect accuracy and not damage, etc).