I think it does suck for people already on Grob that they don’t get to make the choice. Not everyone there is necessarily a die-hard PvP ruleset forever player, but their server got chosen as the sacrificial lamb to be the PvP mega-server experiment.
I think if it fails they will then later consider letting them all merge into a single mega-server and maybe offer War Mode as a WPvP option, but that could be months from now if it ever happens.
They should let them choose now and if Grob’s population is devastated by it, that will just show you what the majorities priorities are faster.