Just my 0.02€, but using gzip on the conenction would likely be more effective than special protocol support for rectangular areas. Likewise animations.. I analyzed a few streams and found that animation bandwidth use can be reduced to a few bytes/timestep that way. The computational effort is also comparable to implementing special protocol extensions like filling areas.
Compression would be more efficient, easier to implement and more stable. IMnsHO. pcg@goof.com