Thank god i didn't wait for them, i just rooted my phone and installed the rom, works fantastic now, no lag issues at all.
T-mobile knew the phone was laggy when they sold it to you as it was already mentioned in reviews, once they heard HTC were going to do an update they should have been on the case, orange already have the update for their phones, so it can be done and alot quicker. Sorry to say T-mobile has no excuse for the delay.
As far as invalidating the warrenty, make a back up and you can always flash it back to the old stock rom.