I've seen this so many times - rather than just write code to do something, wouldn't it be grand if the users could plug their code in with some scripting langu

I've seen this so many times - rather than just write code to do something, wouldn't it be grand if the users could plug their code in with some scripting language or twiddle some configuration and poof! magic! new features just happen! It's one of those things that looks grand on the whiteboard and fantastic on the slide deck, but holy fucking christ when it comes down to implementing it and moreover, having to support it forever after, the pain spirals. Users can't actually implement their plugins, so you end up writing them for them, in a gimped DSL or scripting language, and all the initial choices that were made become ossified, because you then can't ever risk breaking some potential plugin code out there that depends on the API.