I recently made a suggestion about adding a "decapitation" enchant to increase mob head drops, check it out by clicking here out and upvote if you like the idea!
Specifically regarding increasing mob head drops, it definitely would make Slayer less of a tedious job, and more rewarding. Although, I would suggest that a Trench-style restriction could be applied to it, to make the prestige of completely levelling Slayer not entirely useless.
Currently, Slayer takes a lot of effort and a lot of mana, for not really many rewards. I, personally, am only levelling Slayer so I can place my own spawners. Perhaps the whole mechanism of Slayer levels and their associated requirements could be.... reworked?
I'd have to think more on it to come up with some ideas, but it seems the community have some amazing small ideas that could be brought together for a whole new experience.