I would be fine with it, as Vivi actually shares an extremely solid bond with 6/10 of the crew. A bond that actually doesn't feel forced as it was build through the entirety of the baroque works saga. I don't think power isn't even that much of a problem, as Oda could just give her a powerful devil fruit (she never had a 1 vs 1 so changing her fighting style wouldn't really affect the character much, kinda like Nami going from bo staff to Climat tact)
This is assuming Vivi didn't get captured though, as Imu showed interest in her.