Give us old Freeport and Commonlands and DBG will see the biggest sub numbers for a TLP ever! Shit throw in a Kunark start and their servers will melt.
The problem is that they can't revert Freeport for an event server without doing it on all servers. Which would be great if they did that, but waaaay too many later quests are tied into New Freeport. Those quests would be totally messed-up by a reversion. PoR would be thrown into chaos. Yeah, a small price to pay, I know.
Ideas for event servers:
-Kerafyrm - Start at level 50 in Velious with Luclin and PoP unlocking after 2 and 4 weeks respectively, goal is to be the first to get to 65, gear up in Time, and defeat the Sleeper (who gets reset 30 hrs after each awakening once PoP is unlocked, or something). Without GoD gear or level 70, defeating the Sleeper would be a serverwide, 100-person effort type thing, and only attempt-able several times a week.
-Kerafyrm (alternate) - Server starts in TSS with everyone at level 1. We've never had a server like that, and TSS is the last expansion to have content all the way from level 1 on up. So it'd be a brand new experience. You could even have this be a regular server and go from there. For the event server idea, the goal would be to reach level 80 and be the first to defeat Kerafyrm in Crystallos. Buried Sea and SoF unlock 2 and 4 weeks after server launch respectively, so similar idea to the other Kera server. This one is interesting to me because you're using TSS zones to level up as a group, plus TBS will now be leveling content (which means the instances there get a lot more use). You've got more levels to cover in one month than the other server (80 versus 15) but it's offset by being on the TSS exp table which will probably balance it out.
Sebilis server: Classic and Kunark both available at launch with a level cap of 50, everyone starts at 1, goal is to be the first to defeat Trakanon under those rules. Trak is instance-only to force people to win the fight with 54, thus making it a guild competition rather than a server effort like the first Kera idea.
The third one would take the most programming adjustment (and may not even be possible) while the other two would be pretty easy to implement. The second one is the one I see as being the most doable of the 3, and being a 75-80 cap situation it'd kinda pick up where the Quarm event server left off.