I'd love to play a more metroid-style Mega Man X game, with armor pods acting as save points, weapon energy replacing missiles, dash for speed boost, ride armor able to be used in most areas for terrain traversal and modification....you guys get the idea. I do realize it'd basically just be metroid with a blue male samus, but hey, it sounds cool in my head.
As for that FPS X that will never happen, my only dislike about it looking at it was the silly disarming opponents. The rapid fire buster looked cool, the overall look was sleek, you could easily see the armor integration in weapon variations and movement upgrades like sprinting and double jumping. Honestly, it'd probably be similar to metroid prime as well, but this isn't really a negative.
All this mega talk is making me wanna go back to an old X game or maybe legends. God this series had some real shiners.