I'll try to explain the rationale behind it being my number one on the wishlist. In my setup these days my MC server runs on an Orange Pi 5B (which is very fast, especially compared to a Raspberry Pi 4B) and I run it headless with one of those HDMI dummy plugs with a spoofed resolution of 1080p. From there I can remote into the server from any PC and make changes (add new media to MC, update the Orange Pi, etc.). The MC server I have the columns setup and sized for the dummy 1080p monitor, so there's no horizontal scrollbars on the bottom and everything fits nicely on the screen...
However, I have two MC clients, one connected to a 1440p monitor and the other connected to a 4K TV. As you can probably guess, if I connect these clients to the server, the column sizes it gives for both are inherited from the spoofed 1080p the server uses, so on both 1440p and 4K there's a lot of extra space in regards to columns and sizes, which because clients don't retain their own column sizes if you resize the columns to fit both 1440p and 4K then close the MC clients and re-open them, those client column size changes aren't retained. You can imagine it can get kinda annoying dealing with clients connected to monitors and TVs with larger resolutions than the server MC is using.
I'm not sure how easy it'd be to do though, because there's things to keep in consideration. Like what happens if you make changes on the server (e.g. add new columns, remove columns, resize or move columns, etc.). Would that mean any customization you've done on the clients is automatically reset to reflect those changes? Or on the other hand, if you wanted to reset the column sizes on the clients to use the default the server is using? It might get messy, not really sure.