A cycle with something along the lines of 2 normal maps, 1 (good) custom map should be doable. I know some public servers (Hampshire Heavies comes to mind) that handle it this way and they're practically always full when there's a normal map and at least 16 people carry over to the custom one.
Another community called Band of Lovers do a custom map evening once a month, where they only play some chosen custom maps which the players can rate, and based on the rating they will put the most popular custom maps into their ragular mapcycle. They also usually have around 16 players minimum at any given time.
Capture the Flag
* 2Fort
* Double Cross
* Sawmill
* Turbine
* Well
Standard Control Point
* Badlands
* Fastlane
* Freight
* Granary
* Well
* Yukon
Attack/Defend
* Dustbowl
* Egypt
* Gorge
* Gravel Pit
* Junction
* Steel
Territorial Control
* Hydro
Payload
* Badwater Basin
* Gold Rush
* Hoodoo
Payload Race
* Pipeline
King of the Hill
* Harvest/Harvest Event
* Nucleus
* Sawmill
* Viaduct
I striked all the maps that I think 99,9% of all people won't enjoy
I'll try and do some research which custom maps I played and enjoyed in the past and post them here.