Technically, there already is. The absolute lowest an item will go is its High-Alch value. Since all bosses are guaranteed to drop something each kill, there will always be a minimum drop for every boss.
There's an element of luck when it comes to drops and not everyone has the same luck, but we all have the same base chance at the drops on the table. Some runs may be disappointing, but some others may make your day... your week... your month... or even your year!
I may or may not have realized that a friend of mine (we're not even friends anymore really), not me, but a friend of mine may have not known that the dragon and vindicta drop their drops separately and the dragon always just drops a dragon bones and vindicta drops his own stuff to the side.