The Ultra Ethernet consortium work is interesting to me, but I’m still on the fence about some of the design intentions or at least considerations. One of the major bullet points they list on their introductory white paper is that they want whatever UltraEthernet becomes to be reverse compatible with standard Ethernet. IMO, if you’re going to go through the pain of addressing the entire protocol stack from PHY up to application level, then you might as well rip the bandage off all at once.

These massive scale networks that suffer from Ethernet’s “inefficiencies” aren’t likely to deploy a mixed environment. They’re much more likely to build an entirely new environment, decommission an old environment, and build another new environment in its place. The odds of overlapping the two seem really remote to me. But then again, having 1M device mostly flat broadcast domains also seems like an odd choice to me.