I'd by tf2m merchandise, if it shipped overseas...
Otherwise, i think the hats just look to tacky and gimmicky, and it's and extra thing to have on the website code. Plus the whole 10% thing would be hard to organize. And eventually people will get tired of it. And then people will complain that tf2maps has lost it's art style, and people will complain that hats affect performance and people will complain because they feel like it, while in the meantime more and more hats are produced, and it's really really easy to do. And then someone will skin all the hats so it's a single invisible polygon. And then the forums will split into hat lovers and hat haters, each of which believe they are the elite and the true tf2mapians. And then tf2m will turn into a forum based hat simulator... Seem familiar.
EDIT: Also the hat sticking out of the avatar thing wouldn't be hard to do, all you need is to make your avatar a bit smaller, then add a top section with the grey color of the side, then stick the hat on. Then Voila, it's obsolete.
In summary... NO