For reference: Apple's Dishonorable Records for Intel currently stand at:
Fastest drop from introduction:
- #1 4 years, 5 months (Early 2008 Macbook)
- #2 4 years, 6 months (Early 2008 Macbook Air)
Fastest drop from replacement option:
- #1 3 years, 3 months (2007 Xserve)
- #2 3 years, 4 months (2007 Mac Mini)
Fastest drop from discontinue:
- #1 1 year 11 months (2017 21.5" iMac)
- #2 3 years 2 months (2017 Macbook Air)
The MacPro7,1 might not be guaranteed MacOS 15 support by Introduction date, but the 2020 5K iMac will make it into MacOS15 implying Intel support. Suggesting Apple will support the last iMac but not the last MacPro sounds implausible.
Going by discontinue date suggests the MacPro7,1 will support new releases of MacOS at least until May 2025. Again, MacPro7,1 will run MacOS 15.
Counting from 'replacement option' might imply support out to September 2026: good enough MacOS 16 but not setting any records if dropped by MacOS 17 with an October or November public release. However if Apple considers the 2022 Mac Studio a valid replacement option the countdown could expire June 2025, only good enough to guarantee MacOS 15 support.
Apple might be willing to break one record but I don't see them breaking all three. So, 100% chance MacPro7,1 will run MacOS 15. At worst Apple might pull a Mojave and drop Polaris/Vega drivers, but MacPro7,1 will have an update path into MacOS 15.
As for MacOS 16... lets see if the Late 2018 MBA and Early 2019 iMac receive MacOS 15 support. If both do the odds are good. If both get dropped then MacPro7,1 is probably getting cut from MacOS16.