A couple thoughts:
A selectable random chance for a 'diplomatic incident' resulting in a war between two truce-NPRs or between a player and a truce-NPR might be interesting. Players can RP this, of course, but not knowing when they come can throw a curveball. Though they're still going to bombard planets into extinction...
![Smiley :)](https://aurora2.pentarch.org/Smileys/classic/smiley.gif)
re: Underground Infrastructure.
I like this sort of thing, I usually house-rule out Terraforming so I do a lot of 'hostile colonization', even normally. ..
so now we have a sort of tiered colonization:
gas giants - OH
rocks - UI
hostile worlds - Infrastructure
Hmmm.