I feel like we've been burned by interpreting stuff from Hearthstone so many times at this point that it's kind of a suicide mission, lore and plot-wise, to expect anything from Hearthstone to have any bearing on WoW whatsoever. Sometimes concepts or aesthetics or characters appear there first, but more often they appear there and never in actual WoW.
I don't think WoW players of any kind would be really very happy if the game suddenly became spaceship-focused. It's fine for them to be used for transport, as backdrops for battles, and so on, but I don't think they could really be a much bigger thing than they were in Legion without beginning to push people away from the whole WoW vibe.
Metzen's idea of "ridiculous" is pretty broad so it's hard to read much in to that.
Whatever they do, I expect they'll be aiming for a massive "reset" to more standard WoW-style fantasy* after The Last Titan, together with a level squish. If we get a real world revamp, it'll probably be then.
* = which is not "medieval fantasy", I have no idea why people say that, it's always combined elements of steampunk, D&D-style generic fantasy, heavy metal and prog rock album covers, late 1990s Image comics, revival-era Disney, and more.