Well, if it's in there, it's so well hidden it would qualify as an easter egg (and we all know how much Steve loves those!).
Mind you, info gleaned from rumour sites (even from ones as reputable as AppleInsiders) should be taken with a grain of salt.
I can detect no functional difference between whatever version of TCP/IP I have at home (with 8.6) and here at work (9.0). There are no cosmetic differences, either.
A quick shufty through the online help shows nothing regarding multilink, and multi-homing brings up all sorts of irrelevant stuff.
So, I guess the answer this time is wait for the next release.