Are there any RFCs describing the above requirements?
Couldn't find any. I guess you're not interested in RFC 1794 ;)) [...]
So this looks like "host" spec could be the starting point of new spec?
I would say LB MUST conform to "host" spec. Those load balancers that provide routing functionality MUST conform to "router" specs.
We could put all *NAT* and L4+ stuff in optional requirements. Probably the goal is to describe IPv6 load balancer, that would work in IPv6 only environment and IPv6 only clients and servers. Am I wrong?
Load balancing between IPv6 clients and IPv6 and IPv4 servers (6-to-6 and 6-to-4) is a short-term MUST. 4-to-6 is a longer-term SHOULD. Mixed v4/v6 servers behind the same outside virtual IPv6 address is a SHOULD. Support for X-forwarded-for (or equivalent) header in HTTP is a MUST (otherwise the servers lose any visibility into who the client is). I don't think you can specify anything more than this. Ivan