BLU should be scaled back though. It's growth format is purely cumulative, whereas regular jobs have a set 32 maximum skills, BLU has 80 and growing. It can't be sustained. BLU should be getting fewer spells with each update anyway, and eventually it'll cap out when it gets too big.
Where will LTD job development go from there? Into other LTD jobs.
Balancing Beastmaster with BLU content will be many times easier than balancing other content. BLU is already fairly unbalanced, with most of the difficulty coming from the innate difficulty in using and coordinating it's skills. Which is why gaining the Morbol mount can be both far easier or far harder than those same savages on regular jobs on ilvl, depending on your party.
It's more in line with Bozja and it's Lost Actions, which enable people to essentially become any role as their own job.
Balancing Beastaster with BLU should be no more complicated than balancing a Tank WHM with a Healer GNB in Bozja. And yes, I've seen WHMs tank the entirety of Castrum Lacus Litore.