From a pvp standpoint I think gliscor + excadrill deserves forms due to them being great for generations in pvp and generally flexible on teams. It would provide more motivation to hunt these for building teams as well as getting the chance of the rare event form.
From a personal bias view I think solosis, shellos, deino, pinsir, venipede, shroomish and aron deserve event forms as i believe all of these pokes are not hunted alot due to there being generally better options in pvp but are still good nevertheless. I think giving these pokemon event forms would motivate people to hunt these underrated pokes.