I'm personally on the fence about this due to the only custom pets that are in game aren't of current mobs, but please correct me if I'm wrong on that?
Though I do think it's a good suggestion overall and seems to have a lot of community support. It would be a sick pet. I just worry that it opens the door to so many more custom pets that aren't in OSRS, that maybe aren't all necessary, such as barrows pets, moons of perils pets, etc.