Atoon, making a map for the Main Arenas is incredibly complicated. You need to get the field placing even, you need to get the strat working correct. you need to please buffers, base takers, furballers, GVers, mission flyers, lonewolfs, providing possible fight opportunities for everyone.
Like HT has said in the past: HTC are very busy finnishing the last touches of combat tour. Want them to go mapmaking *instead*?
Yes, HT accepts custom maps for the MA. As long as they fit their criterias for the Main Arena. If you plan on making one, its best to browse the board, there are multiple threads on maps that were in the making before the changes, where HT chimed in and stated what he required of them. Its also recommended, that once you have an idea outlined, to check back with them by email (before you go through the laborous process of building the map and not have it accepted because of layout/objects).
Check the Terrain Forum for help if needed. Denholm made a guide on how to use the Terrain Editor (if you need that).
PS: BTW, we have at least two new MA maps since the change: Stall and Beta2.