I didn't really look too hard into composing cause I wasn't sure it was a for sure thing. Could you give a few more details about it? Such as what you get for extracting certain items .. etc.?
Also, will all the buffs be available for the custom potions? What level will the buffs be at? Does Distil work on them?
Much left in the open.
I think gist of that feature is to get a component (call it a 'shard' for the time being) by sacrificing an item on your bp, based on that thread probably a higher class of item will yield more or better results, you should get more value from sacrificing an LE item compared to a 'rare' item and use those components to make into a potion.
What buff do potions give are still undefined and what to get from sacrificing are still subject for discussion i suppose.