It's feature complete now, and we're writing the paper and book about it. So it's ready for early adopters to start prototyping with. Lots of folks already doing so and discussing here: https://forums.fast.ai/c/fastai-users/fastai-v2
Not sure when the final version will be released. Main thing we need to do is cleaning up the docs.
We have solved this problem by providing 2-way sync between notebooks and libraries, using a system called nbdev:
https://www.fast.ai/2019/12/02/nbdev/