While I know people really REALLY want a new Last Stand mode for Dawn of War III (as do I), I've accepted that it's not really practical outside of Dawn of War 2 given the way that Dawn of War 2 had it using Wargear.
I know there could be a set of doctrines and setups for the possible Last Stand mode, but I think putting in a full on Horde Mode would be better. Dawn of War 2 had an exceedingly awesome Last Stand mode because of how much direct focus they put on the hero units and basically minimized armies, I think setting up a large army version where the difficulty ramps up over time would be an even better prospect.
Right now most people dislike the core mode, and annihilation isn't on the quickplay but if fixed it'd be more popular. A simple horde mode would enable us to test our skill, if you include some random enemies here and there to shake it up and prevent solid build/patterns then we could even see it become competitive.
There are some people who've made a semi-horde mode series of maps, where you go up against 3 Ork AI in a citadel style map, but it's crude and not really effective with more than one player.