"They lost the source code for Daggerfall"
How do you lose source code?
What the hell, bethesda >_>;
It's
rumored that they lost part of the source code when they moved from Bethesda to Rockville.
I think it's unlikely they'd release them either way. Daggerfall had plenty of quirks and bugs and they wouldn't improve by porting the game over to a foreign OS. As for Arena, it's already available for free for PCs, I have to wonder if they'd recoup their costs of porting it to a handheld.
Rather than porting a game Vir2L (the TES Travels developer) could spend their time developing their own game. That way they don't have to worry about making compromises between what the device can handle and what the original game was trying to do. They also don't have to worry about the difficulties of porting. Because of this I think a new game for one of these devices is far more likely than a port.