Square milking FFXV is a real possibility, sure. That depends on reception of the DLC episodes and sales figures.
A game for Kingsglaive? Hmm well if it's a new story on the Glaives and not a retelling of the film in a game format it'd be ok.
The events in the movie wouldn't translate well into a game. The only playable part would be the last 3/4 of the film.
To get back on track with the thread topic, adding in diamond weapon and possibly ultros would be a fun idea though. That's about all from Kingsglaive that should be transferred over into game format but that's just my opinion of course.
To be really honest when I first heard about the Versus XV rumor especially from 4chan I thought it was BS(the rumor included the Kingslaive game BTW), but when you think about it Crystal tools(Which was another engine Square had troubles with hell it's the reason Luminous happened in the first place they tried to make FF Versus XIII with Crystal tools and it couldn't do it and possibly ps3 limitations) they got 5 games out of it FFXIII, XIII-2, LR:FFXIII, Dragon Quest, and FFXIV 1.0, I don't see them just putting the world of FFXV down and moving forward to FFXVI especially if they reach that 10 million units which is looking pretty likely at this point I mean 5 million sales is it including download sales, hell Tabata said he wants to recreate the game for PC, making a superior version of FFXV for it.
Also considering what they do to their more successful FF games they give them sequels, FFX very successful got a sequel, and might even get a FFX-3, FFXIII regardless of what you think of it got 2 sequels, honestly even if FFXV got 8 million lifetime sales, I could see Square not only trying to get a prequel out(Kingslaive game), but they may even try to make Versus XV sorta like how FF Type-0 was a pocket dimension alternate universe to FFXIII, possibly the same thing could happen with a Versus XV, but instead it has more connections to the FNC like fal'Cie, L'Cie, Cie'th, maybe has Stella instead of Luna(don't really care tbh), and Versus XV could be the epic that Nomura wanted to create this (probably) trilogy of games(using sets assets from FFXV) starring the Chocobros possibly after a Kingslaive game?(Don't know how that would work because if they would want to make it more like Versus then Luna's going to be gone from the story and Stella would return(granted I'm not too sure if they will use Stella at this point in time), and they will probably have to change it to a new story). Hell even the Versus XV world in KH3 seems plausible, but only as DLC, not as a main world in the game that wouldn't happen, but considering KH3 is releasing on platforms that have an install base more use to DLC, I could see it happening I mean hell we have Sora in World of Final Fantasy as DLC, so it's not impossible.