This requirement for a domain-specific language (man that's sort of a terrible pun in this context) and limited ability to inflict collateral damage on the server with said language has me considering Haskell (after all, even if you do get eval... you probably don't know enough Haskell to cause great damage). Also, my desire to actually build a reasonable-sized project in Haskell in order to cement my learning of it. In practice, I expect that if I do get around to it, it'll probably be in Python and just not handle a lot of the crazy magic edge-cases, unfortunately. The good-enough is the enemy of the perfect :\
Finally, caphiend has more-or-less finished producing an ACKS SRD by removing the closed content from the ACKS manuals. Go take a look at https://github.com/capheind/ACKS_SRD !
(Man, these sort of posts are really easy to write! No wonder Tenkar does it so frequently d: I have nothing but respect for Tenkar, for the record, but he does post a lot of news. I hope someone finds this post as useful as I have found his).