When I ran my own small business I made heavy use of the catalogue feature of Altium Designer (10.x and then 11.x). The catalogue that satisfied my component need best was Farnell's. Although I could have saved some money sourcing components elsewhere, the amount of work that it saved me outweighed the higher prices.
I think this is also valid for small businesses that use KiCad as EDA package. I don't know how dedicated Digikey is to this project, but maybe there's manpower for creating an script/extension for KiCad that checks the availability of the placed parts via your API.
My 2 cents: Bad idea.
If oyu choose that road, think about adding '_obsolete' at the end. This way alphabetic sorting works better and users see it immediately. Else there will be a big block of obsolete libs in the list and all other from 'P' to 'Z' after that.
Maybe introduce a regime to toss out parts 2 years after they became obsolte or something like that. It won't stop bloat but at least set a limit.