"Wrist-watches" with bullet and health readouts. Just look down at any point in the game and your virtual arm will come up, showing everything that you need to know on the back of it.
Maybe gun models that give a visual indication of remaining ammo will become more popular.
Perhaps adding blur/color saturation filters to your entire field of view might take off as a primary indication of remaining health.
Otherwise, yes, watch, checking gun magazine or condition of a blade, or a PDA/map - gaming is going to take a monstrous step up.
Not to mention immersive story-telling as a new way of presenting films.