[jmull]

Here's what I'm thinking:

You add a homa-like header inside a UDP packet. Inside the data center you use switches, nics, etc that know and understand the home-like protocol and can implement homa-like behavior... as needed. Anywhere else, you can fall back to UDP, due to its ubiquity.

Yes, various things would have to somehow know the homa-like protocol was being used... just like various things would have to somehow know the homa protocol was being used. Yes, different vendors would have to have compatible homa-like implementations... just like different vendors would have to have compatible homa implementations.

I think the complexity you mention is inherent in anything that actually gets more widely deployed and used.