I think we're unlikely to see either.
Arena and Daggerfall are already available for free and almost everyone with an XBox 360 (or for that matter PS3) also has a PC that can run these games. If Bethesda had plans to port these I imagine they'd sell them for the PC as well as these other systems and instead they've decided to release them for free.
Well I suppose they could charge 4.99$ for playing it with better resolution, xbox/ps3 controls and no DosBox, I'd pay for that actually.
Oh and last year Command and Conquer became free off EA's website and simultaneously released for 5.99$ on PSN and Xbox Live, the same has been done with Simcity if I remember correctly, so it's not completely out of the question.