"it seems unlikely that further iMac updates will occur in the near future. "
Broadwell is still as delayed as it was last week --- Intel admits publicly that it won't have the high-end iMac appropriate CPUs ready for at least another six months (and who knows what they're telling Apple in private).
A refresh along the lines of the MacBook Pro refresh yesterday makes perfect sense. Personally I was surprised that the rMBP refresh didn't wait until the newest 802.11ac Wave 2 chips were out. (Broadcom promised these about four months ago, but didn't give a date, so maybe they're also delayed.)
I expect a minor CPU speedbump, like the rMBPs, is a given. Maybe likewise a bump in the minimum RAM. They could also ramp up the GPU slightly if nV has something appropriate.
No-one's claiming such an update is ideal, but the Broadwell delay is what it is, and it make sense for Apple to provide some improvements rather than have many potential buys just delay for another six months.
(Or, to put it differently, Apple is continually trying to maintain a more-or-less constant price for its products in the face of constantly falling competitor prices. They can stick with a fixed price for a year or so, but eventually the discrepancy with the competition becomes too glaring and they have to do SOMETHING to relieve the tension. Mac Mini is one case where they can delay for longer, because their just isn't that much competition in the space; it's not highly visible like the laptops and the iMac.)
