Like the topic says 
With multi-core systems becoming more and more common, this could provide a significant speed boost on certain systems. Systems with hyperthreading might gain a little performance, too.
Maybe a preference could be added to select how many files should be analysed at a time?
I did actually make this task multithreaded, however unlike MusicBrainz lookups where most of the work is done on the server, Acoustic analysis is mostly done on your local PC and is cpu bound, so multithreading is really only of benefit if you have some sort of multiple cpu system otherwise your machine is likely to perform worse.
Because of this I didn’t complete this feature as I was concerned it would cause problems, but Ill take another look when I have time.