I would love to see a L4D/Alien Swarm-style colour parameter on props - I could see myself getting a lot of use out of that with custom assets, and a lot of the vehicle models added in the STU update are L4D2 models built with that feature in mind. There could potentially be some use in applying that tech to xenian landscapes as well, to boost variation in the organic and rock props without creating whole new skins.
That said, even the new models they’ve already shown off in that one screenshot would make me a happy camper (mapper?) so I’m not going to hold it against them if they don’t implement that parameter.
EDIT: Just happened across the Content Creator Request thread, and it seems I already stated my desire to see it and got a confirmation that it was in the works at the time. It was supposed to come out in Content Update 3, but as is often the case for programming tasks, it must have gotten pushed back due to bugs. That or they forgot to put it in the fgd. Either way, hopeful it will be fixed by Xen’s release.