It will be hard no matter how good the E3 is for Nintendo. Hell, they could win it but they'll need more than just that even to get Wii U selling. The damage done cannot be removed easily. They need to get it out of "the line" for casuals. I believe it's too late for hardcore gamers that aren't Nintendo fans to start coming back. Could get some nostalgists by releasing games like Star Fox, but the casuals are gonna be the ones that make or break Wii U.
XBOX ONE/Wii U/3DS/PC
RIP Iwata 12/6/1959-7/11/2015
Thanks for all the great memories!