Add the actual input ItemStack(s) to the BloodMagicCraftedEvent so that we can modify the output stack based on what the input's are from a list of valid items, or what NBT is on the input stacks.
A potential use case is a backpack or other storage that is upgraded through the Blood Altar, and you don't want the user to either lose stuff or have to empty it before upgrading.

I'm more than happy to clone the repo, implement this myself, and submit a PR if time is the issue. I haven't started yet only because I don't want to do all the work for nought, in the case where it doesn't meet your style and standards.