I used to work on a proprietary software package that used this approach. But the original authors of our software underestimated the craziness that customers

I used to work on a proprietary software package that used this approach. But the original authors of our software underestimated the craziness that customers would put into their "config" files. Once they had a programming language, our customers started to write programs. Big programs--like approaching 100K lines. Programs that dynamically did different things in response to environment variables, machine names, specific usernames. Programs that read in custom ad hoc customer-specific "config" files. Programs that communicated to central servers over sockets. Programs that popped up GUI windows. And of course programs that had lots and lots of crazy bugs, from memory leaks to stray pointers corrupting things to security issues. You cannot imagine how much fun it was to debug "our" software when the problem turned out to be in a customer's code. There are some solutions to these problems, but you have to anticipate them first. I guess I'm just warning you to do so.