What is a Player Engineered Networking and Interfaced Server:
Essentially it would be an option from Blizzard to allow players to have a private Classic server (sanctioned by Blizz) that can be Vanilla, TBC, WOTLK where the only thing Blizz does is collect the subscription fee, everything else such as moderation GM responsibilities, dev tools, are on the owners of said server.
Pros:
This will allow greater testing of WoW Classic and allow players to have a stake in the direction of where Classic goes and you may get many new game styles out of this.
Additionally, instead of people making post every day for a TBC server and Blizzard having to decide what to do next for Classic they can allow players that ability to manage a TBC server.
Cons:
Similar to other pservers, corruption, drama, exploitation will definitely be an issue if not clamped down on and Blizz would need to have some oversight to stop these issues from happening.
Additionally, the question of what is the threshold to allow a player a pserver? 1000, 10,000 player petition? Or worse $1000, $10,000?