I just came back from a dump run up here in snowy Minnesota and was thinking the same thing!!! it would be a nice feature that would definitely prove beneficial in keeping the wheel wells clear in the winter time... and doesn't seem like it would take that much to do it!

Two things you can try,
1. Black Magic tire spray (the dressing, not the cleaner) up on all the plastic once its cleaned off. Either that or cooking spray. Either one in an aerosol can works. I use BM on all the door seals, in the areas around the bottoms of the doors. Anywhere water can collect. It works pretty good on the wheel wells. Since silicone is hydrophobic, it doesn't give water or slush anywhere to stick to, and nothing to build on. But if you start kicking up sand and salt, it breaks through. So, it depends. Cooking spray is cheaper if you end up using it a lot. But the idea is very much dependent on how much gets in there.
I tried the experiment a long time ago on one car. I sprayed the drivers side with BM, left the other side untreated. Drove to work and back (30 miles each way over all sorts of bad roads and hills). Got home, and the results were, drivers side had a few buildups around the strut, but only a bit of caked on gunk on the wheel wells. The other side, was built out almost touching the tire.
So, my theory is this...
You could work up a spray can system to the inside of the car with BM, and tubing using some cut down washer nozzles to mist the wells on either side. You would probably have to use the pressure from the can itself, as no pump I can think of would sling that crap.

Its a modified process of delivery from what I have in my 87 Regal .It has a rear tire misting system to help dump water on the drag radials on the street. Standard washer pump hooked from a small 1L soda bottle, washer nozzles diverted to either side, spraying out just ahead of the rear tires. Button in the dash would turn the pump on and off.

Yes, I mist my rims with BM as well. Gets expensive, but I buy on sale then store it. You only need it for winter anyway.

Its similar to the idea of using WD40 to dry out electronics, such as rotors and caps because it is also a formula that "displaces water", though its more of a mess and doesn't hold up to protection as long when you're talking wheel wells.

I think you need to look at something that doesn't rely on heat, just something that is hydrophobic as a coating. Its much more cost effective, doesn't require major alterations, and its simple to just stop spraying it when it isn't needed. So no major headaches switching to "summer mode".

Try it, I think those of you really getting that junk caked up in there would really see a benefit.

2. For the caked up wheel problem, there are these dust shields that fit inside a certain diameter wheel. Mainly, they are used to cut down on brake dust getting onto your wheels. But, they also serve a purpose in slightly making your brakes warmer, and keeping colder air out of your wheels. So the brakes effectively melt off whatever collects in there. Plus I ride the brakes once in awhile, when I'm first getting moving in the morning, just to try and build a little heat in the pads to melt off anything that settled there overnight.
Just though I'd share my ideas, driving in upstate NY winters for more than half my life right now, with every type of vehicle you can imagine.