We have seen tomb raider on the GBA. Amazing work, wow.
Is it possible with magic and the star aligning to port mario 64 on the gba and if yes should we dare to do so or is it a better idea to keep pandoras box closed.
It could be done. Mario 64 is not a very well optimized game so there is plenty of headroom for optimizations to be done that could get it to a playable speed (depending on what your definition of playable is) - if you've seen Kaze Emanuar's videos, you'll know exactly what I'm talking about, but sadly, the optimizations he made are very N64 specific, the GBA hardware would need its own set of optimizations, so they aren't very useful here.
It would not control very well. Mario 64 DS controlled pretty badly and it would be worse on the GBA with no touchscreen. But it would be playable.
The GBA has no 3D hardware, but fully 3D rendered games have been done on the GBA even commercially, such as Payback:
You might notice that the framerate of that game is pretty low. Which might be less than ideal for a platformer which requires faster reaction times. But it probably isn't perfectly optimized, so there might be additional performance to be gained.
Some things like the Mario and enemy models could be changed to 2D sprites (Doom style) to gain more performance and might be necessary in order to have playable performance. But I'm almost sure it could be done by a talented enough coder.
I'd question if it wouldn't be a waste of their talent for a subpar end result that would no doubt be the worst way to play Mario 64 though. If I was that talented, I know I'd have better things to spend my time on.
I dont know. I doubt this is the level viewer. But it shows that the dream is real, will it become reality?
I think that's someone trying to recreate Mario 64 from scratch and not doing a very good job at it. They've modeled a (not very convincing) facsimile of the outside of the castle and created a basic walking simulator to allow you to walk around in it. That's a very long way away from a full recreation of the game and they probably never intended it to be a full recreation (Edit: Reading the description of the video, they indeed didn't)
I doubt they used the reverse engineered source code in any way, they probably just looked at screenshots or gameplay and tried to recreate it.