I think that 14 will still support some of the late Intel machines, but as we are getting closer to the finish of the Intel to ASi transition, I wouldn't be surprised if macOS 15 is ASi only.can't wait for macOS 13.5.
Then it all slows down for the next 2 years cause macOS 14 is gonna just be a bug fix party. and most likely Apple silicon only.
The supported machines list will probably look like something similar to this:
I think that they would want to get rid of anything older than 9th gen Intel (given that Apple got rid of support for Skylake/6th gen Macs with Ventura, but kept Kaby Lake/7th gen even though the architecture is the same).
The iMac Pro will probably stay for now, similar to how the 5,1 Mac Pro (2010/2012) is supported on Mojave if you upgraded the GPU to one that supports Metal.
Support for the 12" MacBook will most likely be ditched. Great form-factor, but the CPU performance is horrendous compared to even older Macs.