Aka: MML3's going to be the biggest fanbase tease in existence as it goes down in flames after having been built up to nearly Duke Nuke'em Forever proportions in terms of engine/game readiness?
It's almost a guaranteed "won't happen" because of the timing. The 3DS hasn't had nearly enough time to saturate the market enough to get enough players to show support for this. With summer coming up and gas prices hopping through the roof wallets are going to be tighter than ever, so I don't see 3DSs becoming a wide spread phenomenon until Christmas at least. Something like MML3 would need to be tested pretty much while the 3DS is at system saturation because the Legends split off has always been such a fan base divider.
For every person that loved MML 1 & 2 there has always been another roaring that it's the worst thing to happen to the Megaman franchise in history. Heck you even see major gaming outlets like Gametrailers touting it as the worst Megaman game of all time. Some people take word of mouth from outlets like that quite seriously; so even with a widespread audience MML3 would have an uphill battle if it's survival is based upon how well the prototype does. As is now...I don't see it surviving.