I was thinking it would be rockin' to have a Monarch-Class Exploration Cruiser and Magellan-Class Advanced Research Vessel upgraded to Fleet Dreadnoughts.
The Monarch would look pretty much like the Galaxy version, but with hull down armor-shrouded cannons on the saucer.
The Magellan would either have a third Nacelle bisecting its mission package or get quad-nacelles like the Heavy Cruiser. It could be retitled "Advanced Technological Warfare Vessel" to keep it true to its scientific roots.
These could also be C Store ships, but if 4-6 fleet modules were required to build them, Perfect World/Cryptic would still get there monies worth out of making them.