Do you think anybody would be interested in a 2-part mold to make AR mag bodies and followers out of plastic resin?

Here's how it would work:

You've got two halves of a mold. They're made of hardwood or aluminum or something. You give it a spray with "Pam" cooking spray (or whatever it turns out works best) as a mold release. In a paper cup you stir up some plastic resin with a popsicle stick, and pour it into one half of the mold. Sandwich the two together, a little resin oozes out the sides, you clamp it together and hold it for a couple hours as the resin hardens. After lunch, you pry the mold open with a screwdriver and trim off a couple little bits of plastic on the edges and you've got two halves plus a follower for an AR mag, that you then glue together just like your kid's plastic b-52 model airplane he bought at the grocery store. Depending on which state you live in, you could then use it as a repair part for another mag you already have, or you could come up with a spring & floorplate and you've got yourself a mag.

Let's also say these molds were either given free to anybody who wanted them, or for just a couple bucks to cover costs.

I'm sure it's at least a gray area in CA, if not frowned upon or worse, but there's a lot of other states in the Union too. Of course nobody would want the user to do something illegal.

Is it:
cool?
not worth the effort?

Not worth the effort.

[doj]
However as of January 1, 2000, it is illegal to buy, manufacture, import, keep for sale, expose for sale, give or lend any large-capacity magazine in California except by law enforcement agencies, California peace officers, or licensed dealers.  
[/doj]

First off, new GI green followers are cheap and easy to come by.

Second, there have been many attempts by well funded companies to make "plastic" mags. Very few of them worked out well. Even some versions of Thermolds - and those are considered the best plastic mag - didn't perform well. The problems are almost always due to the shape of the feed lips.

Making a good magazine - excuse me, mag body - isn't as easy as you think.

Quoted: [doj] However as of January 1, 2000, it is illegal to buy, manufacture, import, keep for sale, expose for sale, give or lend any large-capacity magazine in California except by law enforcement agencies, California peace officers, or licensed dealers.   [/doj]

But he's talking about manufacturing mag bodies which is legal as replacement parts.

It's too much work.