You may remember that one time we did a Guild 1v1 Event - and how heavily it was abused. Seems to me that we could run into similar (or perhaps even more profound) difficulties with a betting system in any arena setting.
TBH I don't see a problem with a 2v2 room so much as I see an issue with adding a betting system and then committing to update and develop said system to prevent the inevitable exploits.

As we discuss this, I am developing a version of "Honor" PvP for us to experiment with. While it is certainly a far cry from a full-featured gold wagering system for PvP, it could offer some renewed interest for those who favor old school Dark Legends clashes.