Sadly as I do know this sg plugin I don't think they could implement this without completely redesigning it so -1

 

-1 We already have private PvP arenas, plus configuring the SG plugin to make a private arena would be too complicated.

 

One problem I'd have with that...if the arena is griefed/mis-built, simply for whatever reason not fully closed, players in 'SG-mode' could escape into the main worlds. I could imagine that this would allow some nice exploits...also, a second problem: AFAIK the inventory keeping/exchanging within the same world can be done with the normal SG plugin, but then players added to the town would be able to break the SG arena from inside. Not sure about whether this arena would regenerate or not...

These points were designed for the private arenas being located in towns. Creating a new world for custom arenas might work, but that would probably cause some nice lag and arenas wouldn't be able to be customized by the players applying for them because nobody would have permission there, it would then be a predefined map.

TL;DR: Either too easy to abuse or not really what people would want, depending on how it would be made.

 

-1 would be hard
I do like the idea of having a special SG arena for like ECC donators only or something like that where you could invite your friends to join.

 

Go to eledan and talk to @Ausalu I made a 200x200 sg arena there I'll make more if someone pays me to do it