It's unlikely to be playable. N64 is a bitch to emulate and it only worked so well on the PSP because, much like it was the case with PS1 Classics, some of the hardware was almost backwards compatible and a lot could be virtualized. The 3DS is just not beefy enough and I really think that a PoC emulator is all you're going to get. The N3DS has a better chance if the code is parallelized correctly, but it's not going to be anything to write home about.