Change the pvp system to how it was right at the end of vanilla wow. When vanilla went to 2.0.1, the change in the pvp system was widely regarded as a great thing. This would make it so any player (not just rank farmers and win traders) could attain r14 gear. This would make PvP a more viable way to get good gear for people who don't enjoy the end game pve content. Which would be especially nice on the pvp server since its supposed to be about pvp.
Great article on it here
I know this is supposed to be a vanilla server based on the 1.12.1 iteration of vanilla, but the pvp system has been changed multiple times, so its not like were breaking precedent. Not to mention, the current system was not meant to handle this type of population.