Nanog list uncharacteristically quiet?

Sounds like this would make everything be symmetrically routed.

No. It only means the end system's first hop is symmetrical. The
intermediate systems might packet-stuff on multiple paths, or choose
a different path based on private data, or whatever. My goal is not
end to end path symmetry -- hot potato routing makes that impossible
in any case. My goal is that an end system should be able to accept
connections via multiple providers without needing a routing table
from each of those providers. (Which can't be made symmetrical even
in the average case, anyway.)

Has anyone researched whether this can scale?

I havn't. I know that right now, someone who wants to multihome has
to do way too much work and they cannot reliably send packets back on
the same first-hop as the last-hop they came in on, which makes it
pretty much worthless to multihome unless you break your BGP listener
to use round robin or pseudo random path selection -- and when we did
this it made some things worse rather than better.

Will you handle the case where the interface a flow uses changes
during the course of the flow?

If the link (or ARP) for the current next-hop dies, the route rehomes
among the remaining interface defaults and then rehomes again next time
a segment is received on some remaining-up interface.

I assume this will lead to "round robin default" until an inbound
packet for the flow is received from a new interface.

That's what I remember saying, yes.

Will the "round robin default" favor uncongested or highest speed links?

Not initially. My test environment has a pair of 10baseT links and the
congestion is all after the first hop, where interface statistcs can't
help with local route selection. I won't entertain the above question
seriously unless our initial results hint that it will be time well spent.

I can't wait to hear the results of doing this!

I expect to have an informal report for this mailing list by January 10th.