Restricting 3rd party viewers would have little to no effect... it's possible, sure, although a lot of effort when it's possible, and easy, to insert code at a lower level. Basically, the way that graphics cards work means that they get told "create this 3d shape and apply this texture to it". In this context all you have to do is insert code betwene the viewer and the card (for instance, using GLIntercept) and it doesn't matter what viewer you use, you've got simple and easy access to grab meshes and textures.

The problem here isn't LLs technical inadequacy or willingness to impose technical limitations. It's a fundamental part of the technology to transmit certain information to you viewer (not matter who created it) and that data can always be grabbed and copied and reused. The only solutions are legal and social rather than technical.

Content creators (and I am one) really need to learn to live with the fact that certain aspects of their creations _cannot_ be protected with viewer-based or server-based technology and adapt their business models accordingly.