In my opinion this could be a useful thing to get, especially since most people don't know that faction fly automatically activates. A command for it should cause less confusion and enable people to grind acrobatics as you said. +1 from me
It might not be too easy/a little bit more work to change the code to allow faction fly to be toggled but the content team agreed that this is definitely useful for people to have. Not only does it enable acrobatics grinding but you will also be able to crit out mobs in your base.
Generally not a reason to not have it other than it's gonna be extra work to code.
Moving this to "Under Consideration" for possible future implementation.