Im just going to say this.
If you sit in PF and know the issue of finding a pure healer or shield healer specifically and you can't really go into raid because you can't run double pure healer because you are missing party mits and think that's an issue?

This tank change is going to create a second bottleneck and you are going to be taking way longer to get into raids.

This is such a bad idea. Look they need to change the idea of "main tank" and "off tank" to simply a counter tank style and a non-counter tank style. Maybe barrier/shield tank and raw damage debuff mit style tank. That's it. All tanks need to be viable Main tanking and not necessarily weaker while off tanking.
Besides, if you main a job that is being forced into a role of tanking you don't like playing? Tough get over it according to SE.
Yeah now I think tanks are starting to feel how Astro's felt when they lost Nocturnal Sect and were forced to be the pure healer instead either a shield or pure healer.