Was this ever proposed? Must have been by somebody.

Was thinking if one loaded the last chamber of their starting load with a "hotter" round (more recoil and / or muzzle blast) they would know that was the last shot and it was reload / back up gun / or flee time.

I don't see a down side. It won't hurt follow up shots, because there won't be any. If you did a partial reload you might lose track of where the "hot" round is. But that is an extremely unlikely scenario.