This is inspired from the series DS9 "Tears of the Prophets" and ""What you leave behind" and No Win Scenario.
The Romulans have joined the interstellar community again, so as such PVE should reflect that, enter:
Volley of Thunder
This is based on the Battle of Chintoka, the player count in around 30 players instead of 20. Which if evenly mixed would be 10 of each faction. Imagine, 30 heavily armed warbirds, battle cruisers and Star Cruisers all converging on the planet that's armed with weapons platforms, waves upon waves of small frigates of a random faction that explode randomly (i.e the suicidal kamikaze Jems lol)
Goal, clear out every thing you can in under 5 minutes (like the show).
Then after that you and your fleet are surrounded by enemy battleships once you have broken through the lines (like Dukat in Sacrifice of Angels)
The rest of the time you have to fight your way out and hold your ground for 3 minutes then you win!
The story aspects are Cryptic's thing but i thought it was a good start