I thought the dielectric was responsible for the sound of this wire? The tin coating is to prevent oxidation.
No, it does not melt off and cannot be removed
I'm not proposing to remove all of the tin coating, just the very end were it gets soldered.
It should be very easy to get off with Scotch-Brite, right? It should just be a very thin layer. Copper is a much better conductor than tin. If you remove the tin, the signal will travel from the copper in the wire to solder to the RCA connector instead of from the copper of the conductor, through the tin, through solder, and finally to the RCA connector. It's one less layer of a (poor) conductor that the signal has to pass through.
Have you compared cables with and without the tin removed?