Well, for old console commands there were already reasons against it jacksonmj posted, and for lua there's just too many exploits if that would work, lua can do anything to your computer. Neither will probably be in the official version.
But I might ask Simon about a lua sandbox, only allow certain functions in saves. That might allow for it to work. But I would expect probably still a no anyway, for other reasons.
Auto save start + 'command blocks' = exploits + crashes + trolls + instability
All of the things created are things that devs are trying to solve by updating. If people want it so bad, make a mod, a script; learn some lua on the way.