Makes sense, I think it is a very reasonable possibility. I've got a pre-walked feebas already sitting there (planned on evolving but never got around to it for some reason), but they could force our hands and make a task "walk 20k with feebas" like with what we believe for eevee, but I'm not evolving just in case.
On a similar note, I'm keeping all my wailmer and swablu from evolving incase they do that.