Yep, I didn't want to accuse you of trying to "sneak in" the change. Still, it might break all kinds of things, e.g. distro packages (didn't double-check if it really does), so we'd better be sure. 

If you are interested not in binary compatibility, as done by SOVERSIONing, but in having multiple Assimp versions available to build against, then this change doesn't help you at all because of include files, etc. This is why I am not too convinced that this is a good idea in isolation.

Maybe we should add a flag for a "global suffix" that is applied to the library names, include directory, etc. and set it to the empty string by default?