By 2018 or 2019 there will be a whole new crop of gamers, so maybe a new audience? Of course we will no longer be in the shadows of Saving Private Ryan and Band of Brothers, which laid the groundwork for the popularity of the games.
This is the biggest thing that could see CoH3 getting made. Since the late 2000s there has been a decline in interest in WW2 games. Now this can be attributed to a number of things but the biggest is simply the fact that there are only so many times players can see the same assets and scenarios without getting bored, and most current consumers had their fill of that playing MoH and CoD in the late 90s/early 2000s.
However the new generation of consumers were still in nappies while those games were in their heyday and conversely are starting to get sick of the same pseduo-realistic modern day military games. So they represent something of an untapped market, especially for a WW2 game that doesn't follow the same old Normandy/Stalingrad storyline.
As you mentioned SPR and BoB were big drivers for popularity of WW2 games, and we haven't had anything like that since those were released. Part of that is because the public has less stomach for that 'America, Fuck Yeah, war is awesome!' style of war film, but nonetheless a successful WW2 film or TV series could be a major driver for revival of the genre, given the untapped market I mentioned previously.
Now, where are these big releases? Well we have that Mel Gibson movie coming soon but given Gibson's reputation and the highly questionable casting of Andrew Garfield in the lead role I don't see that doing well. Nolan's upcoming Dunkirk film looks more promising although I doubt it will gain as much traction simply because it doesn't features Americans prominently (but perhaps there will be a badass American agent/commando/pilot shoehorned in somewhere to fill that gap). I think the biggest potential lies in a HBO/netflix-style big-budget TV series. If such a venture succeeds, THEN I can see CoH3 getting made.