perhaps there are viewers from the gaming industry that can play these files. I'd look there, game engines that are popular may have also developed a plugin for some browsers. The problem is that many of these won't work on a number of browsers, or platforms like some popular tablets. Everything is going for mobile.

web3D viewers,.... maybe there's something under development or already available as part of html5, or a Java based viewer, you'd hope that almost all browsers would have the ability to accept an additional player installation that's Java based, but there too it's an assumption.