I like this idea to be honest. Personally i'd say that a Company of Heroes 3 just reworked would be awesome with a new engine and coding or at least an updated one.
Well, I don't think we would ever see CoH3. At least not in the coming years, for a couple of reasons.
First, releasing a sequel for a game too fast is not the best idea. That's why Relic released DoW, then vCoH, DoW again, then Space Marine and then they announced CoH2.
Second, in the finals month of THQ, they said that they've been working on DoWIII (I remember them talking about a revolutionary design for the Army Painter with almost unlimited capabilities).
Third, it would be very bad for their reputation if they shut CoH2 down and release CoH3 in a couple of years. "Hey guys, we've polished CoH2 and we're selling it as CoH3". Relic would never do that.
Forth, I think WWII is pretty much used up. Both from a design and mechanic aspects, and artistic and atmosphere standpoint. Unless they totally change game mechanics (e.g going in direction of games like Wargame or some grand strategy games) which is unlikely, and CoH is exceptional because of its unique tactical gameplay.
Fifth. WH40K universe is HUGE. There is so much potential, and I personally am dying to know what the hell is going to happen to blood ravens (The emperor is about to "die" too).
So, IMHO CoH3 is unlikely. Relic is (was) also hiring designers with experience in RTS games (as seen in jobvites) so we can be pretty sure their next game will be RTS.
PS: I was really disappointed with Ardennes Assault. I don't know why they didn't release something like The Dark Crusade (Best of DoW series if you ask me). I woul gladly pay $60 for that. Instead, we got a boring "meta map" with minimum interactions and zero challenge.