I like it… The one thing I will say is that legendary drop rates are reasonably high already. How about each boss adds to the anointed drop rate?
Alternatively, what if killing major bosses improved the legendary and anointed drop rate of rare spawn enemies, eventually approaching 100%? This would encourage you to kill all the main bosses, then go for the rare spawns. When they didn’t spawn, it’d be disappointing, but you’d have had fun clearing all the bosses, and you’d have plenty of other items drop. When they did spawn, even with 100% chance to drop a dedicated item and 100% chance for it to be anointed, you’d have 1/3 chance to get the item you’d want, and then numerous possible anointments, so this isn’t an overly generous idea. What it would do is give Gearbox a way to keep farm times for specific items relatively long while making the experience more rewarding and more fun than the current state of affairs. As it is, farming dedicated spawns involves spending the majority of your time either on a loading screen or running to a rare boss that didn’t spawn.
To make it more friendly to people without a lot of time to play in one sitting, they could make each boss drop some kind of token. Said token could be taken to some (Eridian?) machine that would increase the rare spawn dedicated and anointed drop rates to 100% for the rest of the session.