And we might have it no--in 2020 if the 1.5 KS didn't blow up. Poots has said after this KS content he considers Monster done and wants to do other things. I think he's mentioned that what he wanted to do with Labyrinth was more like Zombicide/Descent, but realized a lot of people really tried to use Monster as an RPG. If Poots comes back to a dungeon crawler, I wouldn't put any money down on previous ideas since it would be over 5 years in the future anyways.
I'd be more worried about what might get cancelled from the 1.5 expansions...
I don't think there is any reason to think anything will be cancelled at this point. They have delivered consistently, they had a good show in GenCon, their FB groups are active... It's just going to take a while (but we already knew that).
The final expansion from the first Kingdom Death KS, “The Lantern Festival,” was cancelled, according to Poots ultimately because he wasn’t able to make it play in a way that was both fun and true to its premise. It is vaguely possible one or more of the 1.5 expansions will get cancelled for a similar reason. That said, it seems unlikely to me, because the 1.5 expansions seem to be mor more structured along well-established “This slots into the game this way” templates, while the Lantern Festival was meant to be a weird final endgame expansion, and when Poots was working on KD 1.0 he was still being much more experimental about how different expansions work, in ways that sometimes misfired (looking at you, Lonely Tree).
If I had to predict a 1.5 expansion getting cancelled for a similar reason I’d say Silver City, maybe, but even that seems unlikely. (Or the Goblin Dragon campaign, as it is a hugely ambitious thing with a lot of moving parts, but that getting cancelled would be so awful I don’t even want to contemplate it....)
No, all the currently-available expansions use 1.0 rules, which means they’re mostly compatible with 1.5 but might create hiccups. The 1.5 expansion Campaigns of Death will update all the 1.0 expansions to 1.5.