For what it's worth, I think you should ship with a carefully considered set of everything.
That is to say, a selection of skills and spells that show off how the basic concepts that most fantasy muds rely on are implemented in AFK. So, a direct damage spell, an area affect, a damage-over-time, healing, spells or skills to add and remove affects, and something to show how one goes about adding tokens or markers that are used and recognized by triggers later on.
Likewise, a selection of mobs which have different behaviors. A few that demonstrate the basic flags, aggressive, guardian, etc... and a small handful with mob progs which do interesting things, and even a couple which use hard-coded special procedures.
Races and classes.... I'd probably strip out all but two races, just to demonstrate how you do racial abilities and different starting areas/languages. I'd implement the classic 4 fighter/mage/cleric/thief classes.
Then there's the areas themselves. I would make an extremely detailed and functional admin area... one which both acts as a tutorial and has control panel type rooms. If you've ever looked at the Discworld LP mud, that's what I'm thinking of. I'd ship the mud so that the first new player becomes the administrator and new players thereafter become builders. If the folks running the game can't figure out how to flip a switch to make new players become mortals... they probably shouldn't be running the mud.
To that end, I would probably make the starting mortal zone an abandoned movie lot, with just a handful of rooms that have cardboard facades of shops and whatnot. Make it obvious that this isn't the real game. Have Mayor Placeholder walk around the streets shaking hands. Call the town Tempville.