I'm going to take the "selfish" approach:
Given a choice between changing the "flavor" of a low-population server, or splitting up a high-population server (like Earthen Ring), I'll take the former. At least with the former I'm still hanging around people I know, and no one doesn't make a transfer who doesn't want to. If ER were to split up, and the DC community were to split with it... I'm not sure what I would do.
Of course, splitting up a server means Blizzard has to buy new machines, which makes it a less likely scenario.