Keep in mind that we still have human judges and juries. Something I say often on this point is that some judges don't want the "perfect" memoranda or brief, they want one that will give them cover to do what they think is "right" not what the law demands.
On the other hand, there is an opportunity. Almost all Federal hearings and recorded and transcribed, and all the filings are public (for the most part). I am sure the white shoe firms have already done this in a proprietary way, but I'd be willing to bet if deep learning were deployed on this enormous corpus of language, it would reveal serious problems with our legal system like if you wear a brown tie on tuesday _this_ judge is more likely to grant your motion. We've already seen things like this in the criminal context, e.g., sentencing is more harsh when the judges are hungry, etc.