If you want to load balance, you can use multiple A records and it works until one of the provides goes down. Symmetry is the intermediate is really hard. First hop symmetry is most of what you want anyway. BGP path selection is hard to defeat. Typically, this means that one connection will be used a lot more than the other.
Incoming connections rotate per DNS round robin.
A full NAT Solution would be easier to manage DEC PAIX may be the only place where this can be used Future work Round Robin for outgoing TCP, QoS is a problem, but may not be worth doing. Diffs are small. No, not really. I think that using DNS for policy is a bad idea. With DYNUpdate, there can be a way to take an A records off line when those addresses are unreachable.