Not sure how something that has not been announced is considered "Overdue". Last I checked Apple has promised no one an update to the iMac.
We like to confuse a rumors with official statements.
Forget rumors, opinions, etc. but look at the computer industry standard for similar updates & then Apple's own history with updates (check MR's Buyer's Guide). These updates are certainly overdue & I'm surprised to read that some posters here actually think it's reasonable that Apple might keep us waiting until June/July.
I'll definitely not be waiting that long. No updates next Tuesday & I'm buying a PC.