I am not a SAN admin but work closely with them. So take this with a grain of salt.
Best practice is always going to be to split things into as many failure domains as possible. The main argument being how would you test upgrades to the switch firmware without potentially affecting production.
But my personal experience says that assuming you have a typical A/B fabric that is probably enough to handle those sorts of problems, especially if you have director class switches where you have another supervisor to fail back to.
I’ve personally seen shared dev/prod switches for reasonably large companies (several switches with ~150 ports lit on each switch), and there were never any issues.
If you want to keep a little separation between dev and prod keep those on different VSANs which will force you to keep the zones separated.
Depending on how strict change management is for your org keep in mind that tangling dev+prod might make your life worse in other ways. i.e. you can probably do switch firmware updates/zoning changes/troubleshooting in dev during work hours but as soon as you connect those environments together you may have to do all of that on nights and weekends.
Can you run more cat6? There are plenty of HDMI over cat6 adapters that work well over some fairly long distances.
There are also plenty of extended length HDMI cables that are 50+ feet if you can fish through the HDMI end. They get a bit expensive at that length because they are hybrid fiber optic but no noise concerns.
USB also has adapters to run over cat6. They are usually limited to USB2.0 but that should be plenty to plug a small hub in for mouse and keyboard.