This is what I'm hoping for most. While I enjoy the permadeath aspect of the game and rarely save scum even from some of the most unavoidable and cheap feeling deaths I've had, if death became less black and white, 100 to 0, or any other analogy you want to use, I think it would be more enjoyable. In X1 a soldier with 1hp and a soldier with Max HP fight identically efficient (assuming same stats) and then once they hit 0 hp they are done. Rather then having this fixed point, using random injury tables to give degraded performance, or even incapacitate them prior to hp reaching 0 adds some depth. Also incapacitation injury could take the place of the seemly random post battle 'revived' mechanic. You could also add more functions to medkits, like painkillers or stims, to go along with the injury types.
Side note: Also make injured soldiers matter. In X1 you can build a med bay day one and from that point most soldiers will be 100% before the next mission if you're not going too crazy. Once you get some armor on a 75+ hp soldier you know he can take a few hits from bog standard aliens and be right as rain in 3 days so you can play a little less cautiously with him. However if that one hit that did 1/4 of his HP puts him out for a full month, and when he returns he has an accuracy penalty from a dominate hand injury then even little hits matter.