Thats one area where I am concerned is the increasing security of the T2 chips. Yeah, having secure data is great an all.You really expect an OpenCore style jailbreak for M-based machines to be available in 7+ years? The Hackintosh community would be thrilled, just don't see it happening. M-based machines are a different beast than Intel-based Mac. If anything, would expect the secure enclave security stuff to strengthen/increase over the coming years.
Would not be shocked to see a T2/Tx requirement for the latest OS version to function at some point in the next 3-5 years if OS support for Intel CPUs is still around. That would impact i9-based 2019 iMac 27" with Vega48 & 128GB RAM without T2, which is probably more capable than base level i5 2020 iMac 27" with T2.
Really, all that I've spoken about is speculative. I would love to invest in a new Mac, and if software support lasts for 8+ years, that's good, 10+ years, even better.
I personally see no reason why software support can't go for 10+ years for a Mac Studio other than Apple's planned obsolescence.