I'm just about to solve this problem; I think I found the equivalent of Loop Browser of year 2017, It's called Ableton Live.
I have been nagging it only for 24 hours, so I don't have all the details down yet, but most of the functionality of Loop Browser seems to be in it, and then ten times more. It previews loop files at song speed, playing along with the already recorded tracks like Logic's Loop Browser. But on Live you can drag and drop a multitude of loops into its window and play them back in any simultaneous combination and/or playback order your heart desires, and you can even record this entire performance on the fly as you create it - very unlike the the Loop Browser. I found where Live program stores its loop files, (it's at System HD/Users/Your Username/Library/Application Support/Ableton/Library/Clips) and put an alias to Loop Browser's user Apple Loops folder (which is System HD/Users/Your Username/Library/Audio/Apple Loops/User Loops/Singlefiles) into it and pronto - I didn't even had to restart Live, all my Apple Loops came right up and ready for auditioning and use in Live. Beautiful!
Since I have been on Live only since today morning there are still two issues I'm working to resolve. First, while tempo matching is dead on, I'm still working on getting key matching to happen too. Secondly, while Live can reportedly feed its tracks into Logic Pro on the fly through ReWire by following the instructions on
http://www.ableton.com/pages/rewire/logic_pro , I'm still working on getting this to happen. (There is a ReWire template in Logic's Templates folder, whose opening nukes half of the obstacles in one fell swoop.)
All in all, if the Loop Browser is giving you the fits too by its inability to manage files, or play them from external HDs through a well-placed alias, Ableton Live seems to be the answer. Its ability to audition several loops
simultaneously was such an incredible fun and creative boost to me, if ReWiring it to Logic Pro remains a problem, after a few more days I might even stop worrying about it. 🙂