Well writing code for this would be banal (all it takes is to retrieve a soldier from the Memorial - you can actually do it quite easily yourself by doctoring a save), but for me an important part of XCom is precisely the fact that the soldiers are mortal. You let them die, they're gone forever, all you can do is visit their graves.
One small improvement request I'd like: armor should be removed from soldiers that are killed & moved to the Memorial. Normally it makes no difference, but if it was a stat-modifying armor, the modifiers stay on a deceased soldier and I think it is inelegant (and in the case of revival/save doctoring, it is required - armor was destroyed, wasn't it, and if you have retrievable armor, it was retrieved, so the revived soldier cannot still have his own "copy" of the armor).