I'm tinkering with a "what if" idea - Romulans learn of the doomsday machine encounters (Borrowing from FASA's "A Doomsday Like Any Other") from pilfered Starfleet records in 2320 and the Tal Shiar send a small team of cosmetically enhanced operatives through the Guardian of Forever posing as Constellation officers. They then hijack the machine, destroy the Constellation, and return the device to Romulus where they study it and learn to replicate its technology. The Romulans are unable to make the neutronium hull but are able to make copies of the machine with normal hulls. Conquering ensues. However, the other races manage to salvage bits and pieces of the technology here and there and eventually make their own versions of the devices. Jump forward about ten years; The Alpha and Beta quadrants are now nearly devoid of habitable worlds because of the devistation caused by small fleets of these devices running amok.
It'd probably work best as an adventure maybe not a campaign setting. I dunno, I'm still playing with it. Any feedback would be appreciated.
"Bad thinking is punishable. Good thinking is quickly and easily rewarded."