Every room has maximum of 2 joined rooms thus forming a one-way-in, one-way-out tunnel-like rooms so in order to expand / reach highways / reach SK rooms going through someone else room would be mandatory (either with force or diplomacy)
Oh, i like this. Should be really simple to do and change the general dynamic up a good bit.
An idea that came to mind was a War for the Underworld (was it?) kinda season, where we have to dig out the rooms.
So basically all (or most) of the plain tiles are filled with constructed walls and paths to points of interest have to be dug out by dismantling the walls there. A random number could be 10k hits on them by default and maybe more/less around certain objects (e.g. 100k at range 1 to controllers, 50k around exits etc.), possibly leaving out certain other spots - like around the sources.
Placing one's initial spawn on constructed walls would have to be enabled and successful placement should probably remove walls on the selected tile and the 8 surrounding tiles, but other than that it should be fairly easy to implement.
Not sure if this would be enough for a whole season by itself, but it could be a mechanic at least.