I think I'm going to nominate the return of some old classics.

-de_prodigy - would be nice to have back (when I won captains it wasn't in the pool)
-de_tides - This map is pure classic, both balanced and aesthetically pleasing.
-de_chateau - This map is pure gold. Brings back memories from the old rotation in '09.
-de_port - a cult classic if you will. All I can say is... DANK!
-de_piranesi - nice map, really enjoy its fulfilling moments.
-de_arcate_release - map I found that gives a piranesi/cobble vibe but neater.
-de_greene - gives the prodigy vibe and could really ad a fresh feel to the servers.

Take these into consideration, they're likely awesome additions to the pool.