Summoning command

I’m sure other people that might want to do all the achievements or bestiary might like the sound of a summon command that summons any mob or monster

Probably not coming anytime soon. The command already exists, but no one has access to it (besides the admins) because it is disruptive.
I don’t think there are or will be any plans to create a new server like Sitems, or something similar of the same effect, with the designated purpose of allowing players to use such a command.