It seems to me that all of the Mac desktops (iMac, Mini, studio, Pro) will NOT be updated on an annual basis. Although I suspect at least one model will be updated with each M Chip generation. Some years it would be a mini and other years it might be an iMac. Assuming the entire product line is updated to an M4, then the real question is which product will skip the M5?
Even if the Mac mini always skips a generation, it means a new Mac mini every two years which is still a lot better than its past history of upgrades.
Edit/update:
Here's a list I compiled from Wikipedia:
2005-01-11: 1.25 GHz and 1.33 GHz G4
2005-09-27: 1.33 GHz and 1.5 GHz G4
2006-02-28: 1.5 GHz Core Solo and 1.66 GHz Core Duo
2006-09-06: 1.6 and 1.83 GHz Core Duo
2007-08-07: 1.83 and 2.0 GHz Core 2 Duo
2009-03-03: 2.0 GHz Core 2 Duo
2009-10-20: 2.26 and 2.53 GHz Core 2 Duo
2010-06-15: 2.4 and 2.66 GHz Core 2 Duo
2011-07-20: from 2.3 GHz dual-core i5 up to 2.7 GHz dual-core i7 or 2.0 GHz quad-core i7 (weird options IMHO)
2012-10-23: from 2.5 GHz dual-core i5 up to 2.6 GHz quad-core i7
2014-10-16: from 1.4 GHz dual-core i5 up to 3.0 GHz dual-core i7 (no more quad-core options)
2018-11-07: from 3.6 GHz quad-core i3 up to 3.2 GHz six-core i7
2020-11-17: 8-core M1
2023-01-24: 10-core M2 up to 12-core M2 Pro
2024-10-29: 10-core M4 up to 16-core M4 Pro
So we got upgrades much more often at the very beginning but with much smaller gains in actual computing power.
But apart from the big gaps in 2014-2018 and 2020-2023, we've always had between an average of one to two years between each upgrade, so I wouldn't dismiss the possibility of an M5 Mac mini in the last quarter of 2025 just yet.
I also realized, doing this list, that I'm still using a Mac mini that's now seven generations behind. And even if it's much slower, at least I have 16GB RAM just like the newly released entry-level M4 Mac mini. That tells you how far behind Apple are in terms of minimum RAM in their computers, my mid-2010 computer being on par with their new model. And remember that macOS is not some magical software. The RAM requirements for things like databases, 64-bit machine code, images, audio and video is the same on all platforms.