Nanog list uncharacteristically quiet?

It could be stream based (address and port), and use a LRU cache with a
planned capacity of 5 minutes, to decide on which interface to use. Sure,
it is more complicated, but anything you add increases complexity.

not so. right now our multihomed web gateways need a full routing table.
that's pretty complicated, for my operator and for my customer's providers.
we're shortly moving to an "interface default" such that all inbound streams
will have their outbound route chosen as the incoming interface's default,
and all outbound streams will get a "round robin default" outbound route
that will then be rebound to the SYN-ACK's incoming route, in case the
original source route is better-reachable by "this" destination via some
other interface, a not uncommon case these days.

this adds about 2 pages of code to the kernel. but it's a lot less complex
than taking a full routing table from multiple providers.

Sounds like this would make everything be symmetrically routed. Has
anyone researched whether this can scale? Will you handle the case where
the interface a flow uses changes during the course of the flow? I assume
this will lead to "round robin default" until an inbound packet for the
flow is received from a new interface. Will the "round robin default"
favor uncongested or highest speed links?

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