Well... I don't know. Nobody knows right now really, we just need to wait < 1 Month to have the IOSU Exploit and THEN that someone tries to do it.
But you need to remember this, Super Smash Bros Melee it's not the same as Super Smash Bros Brawl to play it on HD.
Maybe we will be able to have this only on GC Games, maybe on both, probably we will never see this happening, but still.
Of course I know that SSBB is not the same as SSBM, but I was referring to the GameCube emulation and Wii emulation, all of this assumptions are from what I readed, GameCube emulation should be possible because it has a 485MHz PowerPC CPU, the Broadway CPU is a PowerPC CPU too, just clocked 50% higher, and the Wii U has another PPC CPU with 3 cores, so emulating the Wii/GameCube CPU wouldn't be so much trouble.
In short words, what I'm trying to say is if we get a GameCube emulator for HD games, a Wii emulator can be done as well since the Wii is just an upgraded GameCube with few differences and Wii U CPU is a upgraded version of Wii's Broadway as well.
The real problem is the GPU, because games use GX (which is the equivalent to the Hollywood Wii GPU) and that means GX doesn't have HD capabilities.
The main Wii U GPU is GX2, but is a new arquitecture, and there appears the problems...
I don't know what to say about RAM, but since has part of Wii hardware and at least 32MB of eDRAM I don't think it would be so much trouble...
EDIT: I think it would be enough to take the 2 GB DDR3 and put some latency/reduce the bandwidth from 12.8GB/s to the Wii 5.6GB/s bandwidth... and use the rest of the Wii U hardware to simulate the Wii one, for example the 32MB for eDRAM and these things, but like I said, with the RAM part I could be (Is very probably) speaking bullshit .