They're pretty popular for file servers, but if you're looking at several bays and many terabytes, I would recommend looking at "prebuilt" solutions. At the end of it all, you're going to be limited by the Pi's USB bandwidth, network, and limited processing power. I know there are several reviews of the other Pis for these projects, I'd imagine there are some for the 4 as well.
I attached a couple USB HDDs to my Pi 2 running Raspian for awhile, just for movies and some other work, I never had any issues. That is however much lighter work than multiple people accessing larger volumes at once.
I'd like a LTT discussion on it, but the video market for it is pretty saturated already tbh.