I think the main downside of the solution you described, so using single machine for both - production and file server purposes, is that it is more prone to failures than a one-task orientated server.
-3ds max crashes on daily basis,
-renderings freeze,
-there's often a need to install new software etc,
In every scenario above when your machine needs a restart, the files you're sharing with others are not available anymore. That often causes scene/rendering errors for other users.
Also the 100% processor and RAM usage during rendering may reduce the file transfers and read/save speeds for other network users.
So in my opinion, the sole purpose of a file server should be to store, share and backup files.
If you happen to build it powerful enough to sporadically use as a render node too, there's probably nothing wrong with that, and this is what we sometimes do in our studio.
Perhaps tell us more about why NAS solutions and HDDs are not working for you anymore?
Our file server is a Windows machine built specifically for this purpose. It's has an i9 9900K processor overclocked to 4.9Mhz, built on AsRock Z390 motherboard, with 64gb ram.
Probably a bit of an overkill, but as I mentioned wewanted to have a possibility to use it as a render node from time to time.
We only keep the library of assets on a fast M2 drive.
All the projects are stored on 7200 HDDs and we're rather happy with scene opening/saving and data transfer speeds.