To fix the tank supply,there isnt "ONE" solution that is going to fix everything.... its more like several small steps, that are going to build a real solution to the problem.

1)They need to add more tank jobs so people can actually choose from different play styles and find one that is comfortable with them.
2)They need to add incentives for people to play the current tank jobs (the mount thingy, they are already doing)
3)They need to review the mechanics for tanks (a good tank can carry a party, while a bad one can destroy the party, they have WAY too much weight on their shoulders)
4)They need to fix that danm lag issue (call it, "monday lag" "conection lag" "server lag", but theres a lot of people who are suffering this, a tank job relies way to much on dodging, if you cant dodge properly, why play a class that EVERYONE is going to blame you , in case you didnt dodged something, when you can just play a dps, and have less responsabilities).
5)They are way too depdendant on ilvl and gear... while a DPS can maximize their damage output, by improving their rotation, a tank is overly reliant on their gear.

The point, is there there isnt just "one solution" that is going to fix the current issue, its more like a series of stuff that is actually hurting the tank class, and in some circumstances, its also affecting other classes.