I've pushed an updated version of the patch to a new "beets" branch of the EMMS repo.
This version: - ensures at least a name and a type is available for each added track, - inhibits info functions when adding from the beets database, - allows interactive filtering by distinct value(s) of column(s) when adding, - sorts tracks to be added before inserting them into the playlist, - allow customizing the columns to sort by, their order and the sort type, - only gets data from a predefined set of columns, - attempts to fix the data format of some columns and their names, - adds various small improvements and optimizations to the code. This is basically feature complete IMO. I could add an info function which gets metadata from the beets DB if a file has been added without using the beets source commands but is actually registered in the DB, however I'm not sure how useful this really is.
