I'd imagine BST has a pretty high chance of being the melee Limited job class with PUP following it. He's mentioned that they fit in the limited job aspect with BLU , while not concrete, just fits the most. Could be saying that to not basically leak and say "YEP BST IS LIMITED JOB! you heard it here first!"

My guess is that it's a Chain sword whip and they are testing out the physics with the DRK sword. I believe they'd think something too loose like a whip would be annoying to code and flimsy as well as needing sorta a physics animation for it as you run and what not as well as being a bit easier to "Show off" for it's theme when it's as a chain sword whip.

My guess with the pets is that maybe they'd have different food to summon them maybe? work in some way like chocobo but a different menu separate from BST. So you can sorta choose unique stuff for your beasts and load outs.

not saying I think BST or BLU should be limited, just I think they don't see a problem with it since there's more people who like to do side content and random stuff than raiders so balancing a class for raid stuff isn't a push for them to make so many classes to fit in that spectrum.