This is fully an out there, probably not going to happen change that I think would make brig feel impactful without making her absolutely broken.
As it stands, Brigitte has nothing that makes her unique. Moira can survive better than she can, and rally is just a worse junker Queen shout.
My idea: when she shield bashes someone she inflicts 50% antiheal for 1s. This makes using shield bash into a tank more viable, however, with Ana currently having the broken ability that is her grenade, this could definitely not happen.