It occurs to me that if you do plan to expand on sabotage & espionage mechanics 'peaceful' mode might present an interesting test environment. 

I was playing a few games with it on and it was actually kind of stressful - the AI's having avoided conflicts with any of the other Empire's meant they seemed to have functional and sometimes surprisingly modern armies. There might have been a window early on where I had a slight advantage over the other AI's but after about 200 turns I realized what the game mode was reminding me of. The Cold War. Only it was more like a lukewarm simmer standoff. But I digress. I didn't get to a time when there would have been MAD retaliation but several AI's were definitely overshooting me on ERAs and probably tech too. With espionage as a mechanic - sabotage or ransacking that might only be noticed if I had eyes on a resource being ransacked this could definitely still be a challenging game mode.