Unlikely to get a redesign and a CPU only upgrade. Apple really has a terrible Mac lineup at the moment. I'd love an iMac (2014 MBP getting on a bit), but with an ancient design and terrible thermal performance, it's hard to get excited. I'm going to build a PC rig for gaming, and want an average specced Mac as my non-gaming machine but I don't need a laptop, so there is nothing Apple sells that suits that. Mac Mini Pro please.
I feel you. I‘m on the same boat as you, but then again: Maybe it‘ll be a small update that warrants no iMac event.
Or maybe there‘ll be a huge update in Oct or so.
- 50 % more CPU! (thanks Coffee Lake)
- 25 % more GPU! (a man can dream)
- redesigned cooling system (making above possible)
- even faster flash storage, 256 GB as standard (same price as the Fusion drive)
- Face ID included
- newest Wi-Fi standard
- Thunderbolt 4
- available in Space Grey and rose gold
Such things would quickly add up, without a grand aesthetics redesign. Internally, I guess no one would be opposed to a better cooling system or Face ID in the iMac. Let‘s wait for WWDC, and then some more

I mean, it‘s the 20th birthday of iMac - something‘s up for us!
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I was posted in another thread if you wanted a Windows all-in-one you almost would be better off bootcamping Windows on the iMac.
I‘d sign that statement in a heartbeat. Tried some AIOs from HP and Dell over the years - nothing comes close to the overall build quality of iMac. Superb screen, no creakiness, no wobbliness, and boy, is it quiet.