They are thinking of creating a new job unique to ffxiv so lets give them some ideas!

[Ferth]

I know that Engineer has already been a thing, but perhaps a Magiteknician? Could learn from Cid or Nero... It could feasibly fit any role you wanted it to, though I kinda like the idea of a healer who uses machines and a big two handed hammer...

Though most "Pet Tank" idea seem to be "Have the pet tank", and as much as I'd like to see that, honestly think the pet would have to act as support to the player tanking instead, due to a lot of the limitations.

Probably something like the BST doesnt have tank stances, but instead, the pet toggles between doing dmg, or putting a tether on the tank to heal them and raise their enmity.
(And for invuln, maybe have the pet equal you in threat, and then stay ahead of you in hate, taking 75% less dmg until dead, unable to be healed, and reseting their summon action.)

For this game, if they implement Beastmaster as a tank, I would like to see it function more like Interceptor/Shadow. Just give them an offensive pet and a defensive pet and the pet can intercept attacks, give defensive buffs and perform their own attacks. Or perhaps even one pet with a flank configuration for offense and a guard configuration for defense. Instead of an HP bar for the pet have it be the Beastmaster's resource gauge so it doesn't become a convoluted healing debacle.