Just a thought - haven't tried it.

Considering the amount of heat coming from the intake between the seats, what would happen if I was to mount a 12v fan to suck air from the intake into the cab, just to try and get some heat, mostly to hit the windshield

Would this affect the engine air intake ?

[2015 Z Force 800 53/Trail EPS]

If you took the grill off you would see it's wide open behind exposing the engine and all the dust from the tires. Pulling air that direction would increase the heat and dust toward the engine air intake even more and into the cab...something we all are trying to get away from with the Gen-1 Zs. Not to mention additional load on the electrical system. That what all those posts on relocating the air intake and boxing that area off is about.  If you really want some defrosting heat to the windshield I might suggest getting it from the heat off the radiator with a small 2 or 3 inch flex duct and fan mounted behind the radiator and through the firewall to some ports facing the windshield on top of the dash. There would be some fabrication involved but there would be less dust intake. Less..not 100% deleted.

I've often thought about one of these cordless heat guns and a couple of batteries weather it would be worth it for defrosting or not. Have to be careful I suppose.

https://www.homedepot.com/p/DEWALT-20V-MAX-Cordless-Compact-Heat-Gun-with-Flat-and-Hook-Nozzle-Attachments-DCE530B/309138433

As NMK says, putting a fan at the intake grill would create a low pressure area that would increase the intake of dusty air, right where you don't want it.
Right behind the between seats intake grill on the 800 ought to have connected directly to the engine air intake, but that connection was never completed for whatever reason and they just stuck a filter sock on the end of the intake plenum.

For windshield defogging I'd just mount a 12 volt fan directed at the windshield. The airflow will keep the windshield clear of fog.