Develop a programming language which allows you to easily write inline grammars then use them and mutate them at compile- and run-time. Additionally have a nice (default) syntax, nice support for concurrency (I'm thinking something similar to goroutines), and actually try to make the language reasonably popular (the most insane of my goals).

Roadblocks: Myself, more than anything. So hard to work on something a. so big, and b. in spare time when I so often feel like chilling out!