We just released our first offering on KS called Kaiju City and we've been asked about solo play rules.
Solo play was something we had talked about during playtesting. I think the nature of the Monsters' special abilities would make an effective transition to solo play as the city with automated Monsters.
For solo play as the Monsters, you could ditch the resource tracker and draw / play 2-3 city tiles (like 3 resource or 2 resource +1 military Tile) each round and add them in a spiral pattern around the board keeping the city square to automate the City.
We could even have variant rules for Monster Battle Royale where the monsters fight each other as they are being attacked by an automated city.
The real question is, how valuable would this be to the players / potential purchasers of this game?
Let me know what you think!