Also a lawyer here, I think the biggest hurdle is MS Word. MS word is the defacto IDE of the law world. We spend most of our time in Word. The drafting of documents won't be a problem with libre office. You can send a PDF to the client. But working with other lawyers/parties could be a challenge. I am not certain how Libreoffice could handle a 500 page memo being worked by 50+ people including thousands of track chan…
I stumble on bugs in Word Online with far, far fewer participants (e.g. 2).
Confluence holds up very well.