Did he say why? Needing a better power supply, I get... but a board that can run a 1080 should be able to handle a 3080 just fine as far as I can tell. Oh wait... PCIe v3 vs v4. Should still work and be an upgrade but it won't be able to push the card as well as it should. Also, crap. My MB is also PCIe v3. Thanks for making me look. Guess it's whole new rig time. Edit: For me, I mean. And really... it's just new MB, proc, ram and 3080 that I'll need.
Did more digging... : "As of right now, performance improvements to be had when using the RTX 3080 on a PCIe 4.0 interface are very small at best, and in many cases are simply non-existent." Soooo... woot!