I've done it (and completed it) the last five years. I used it to try out a few languages (Haskell, Idris, Lean) and did it in python one year I was feeling lazy. I've got a project going now, and I probably should do that instead.

However, that project is a programming language, so this is a way to test practicality. But solving problems and fixing shortcomings in the underlying language at the same time may be a bit too much. (It's a dependent typed language, so there is a lot of subtlety to deal with.)