YES!!! CAPCOM IS REALLY GONNA MAKE A MEGAMAN ZERO 5!!!
Im going to kill them if they don't really make this!!
Spoilers:

In IGN Boards:
Zero is revived after being blown up in the Ragnarok by Cyber Elves. This revival has caused Zero to intergrate with Elves like never before, hence the new custom elf system.

Plot wise, a new enemy has arisen in Neo Arcadia. Also, X makes a return somehow.

You can find this same info at RockmanPM though I couldn't find it recently. It's in the same post that talks about Intl Creations and their ideas for Rockman DASH 3 and Rockman 9 turned down.