I like shellac's color and ease of application, but the bottom of my laptop melts my table's finish. Yes, seriously.
I'm thinking to cross-link the finish (taking advantage of all the hydroxyl and carboxyl groups) by mixing it with a bit of epoxy or epoxy hardener (polyamine). (Note: shellac is pretty reactive, which is probably one reason it works as a primer. It will crosslink all by itself, if the heat is high enough.)
Do you know of anything else that can be added to shellac to make it cross-link or increase the heat tolerance? I don't like the idea of adding epoxy or hardener because it may have a very short pot life. I might also be able to try mixing it with lacquer. What additives would you try?