In other threads I've seen it mentioned that there's apparently quite a stretch of time between the events of Oblivion and Skyrim, and how no NPCs from Oblivion would be able to make a comeback in Skyrim because of this (except maybe some elves).

Can anyone tell me what sort of timeline we're looking at, and, roughly speaking, what this is based on and how it is worked out?

If this has been brought up before, apologies. I've only had time to have a fairly quick browse through the threads in this section.

It could be anywhere from right after the Infernal City to 200 years after Oblivion. No one is sure and there is not much evidence supporting anything.

No real idea yet. We know from the trailer that it's after Oblivion in the timeline, and we'd assume they've allowed enough time for events in Cyrodiil to settle down, but beyond that is all speculation.