I question how big of a trend it is. I say it's fringe appeal at best. Metal music isn't all over the airwaves, neither television nor radio, like it was back in the '80s. Not by a longshot. Those companies you mention are also almost exclusively known for their metalloid designs. Hamer started out as a big power pop brand, then went metal, then went totally Gibsonesque and now is doing classic, jazzier and mellower designs. They have a wider appeal, which generally is a good thing in business. Besides, why would they want to horn in on a market that Jackson, Charvel, Kramer, Schecter et al have cornered?