[jrumbut]

The coordination problems in creating a system designed from the beginning to be human in the loop is a challenge.

There are a lot of great ML algorithms, even if you limit yourself to 10-20 year old ones, that aren't leveraged anywhere like how they could be because very few know how to build such a system by turning business problems into ML problems and training users to work effectively alongside the algorithm.

CRUD application development projects blow past deadlines and budgets frequently enough. ML projects have even greater risks.

Edit: I hope the people making the successful legal document management system you mentioned write about their experience.

[mumblemumble]

FWIW, my experience has been that, if you're trying to build a system that works in tight coordination with humans, you're better off sticking to algorithms that are 40-80 years old. Save some energy for dealing with the part that's actually hard.