Here's the most useful bit of information I learned today, from some hours of internet surfing:

Metal based body fillers exist. You'd think that after working in a body shop for some time I'd have known this by now.

A notable product is

Hi-Temp Lab-Metal

Hi-Temp Lab-Metal is heat resistant up to 1000 degrees. It can be reduced to sprayable consistency for rust proofing and can be sanded to a feather-edge finish. Unlike normal body fillers, this means it's able to withstand the 400° temperature needed to powdercoat. That means if you're having a hell of a time finding a specific gas tank in good condition, you can use Lab-Metal to fill in the imperfections then send it out to be coated in an array of awesome, durable, finishes.

You may be saying, why not just "bondo and paint?"

Well, in my case, I'd ideally like to find a gorgeous tank that I can take down to metal, brush texture, and clear coat. The possibility Lab-Metal opens up is obtaining a tank with some blemishes, filling them in, then sending it out to be powdercoated in, say "Chrome."

Powdercoated chrome is not the same mirror like, blingtastic finish you're thinking of. Here's a good example of powdercoated chrome, vs chrome plating.

For high road rash areas like fork tubes, swingarms, and fenders, having the ability to smoothly finish and powdercoat these items to a much more durable finish is a great benefit.

As far as being able to plate over Lab-Metal, it's something I'm going to look into more. Now that'd be somethin'.