Originally Posted by Zetr0
I would be surprised if any guarantee would be given with exception to the line of ACA adaptors - and this wouldn't be any marketing tactic - just simple common sense that a company couldn't take on the hordes of support calls for 20 year old equipment.
Exactly. And with FPGA addons, it's even more difficult; I'm pretty sure there are going to be compatibility tests to make both hypothetical products work well together. But one cannot guarantee anything beyond that point - FPGA (core) is going to change, maybe board is going to change, etc.
In practice, whoever is second to release a product will usually be forced to care about compatibility with the first because no one could afford a split in such a small market (again).