Releasing a 3rd Tank ultimately isn't going to affect the # of players interested in tanking.

It's a 'Band-Aid fix' at best.

Tanking with this new class with see a spike for a short time as it'd inevitably become FotM, but that's all it would do.

The real solution?

Do level-appropriate leves with your DPS class while you wait for your queue or make friends with a tank or healer.