As long as they don't [censored] it up I see no reason why it couldn't be done like that, I have no problem with playing past an end as long as there is an actual ending given. Unfortunately Bethesda's past record is Fallout 3's Broken Steel which I believe was a collosal let-down that failed on every level to show any real change - taking place only a mere 2 weeks after all - and one of the two endings wasn't even touched upon at all if you chose it outside three lines of incidental dialouge.
Well way they could do it wouldn't be too difficult, perhaps say a year after events, seeing the jarls whom were replaced and cities that were sacked, perhaps forsworn ask for ya help to overthrow Markarth, these sorta things.