iDrive can handle M3U playlist. This is a how to guide for creating them.
I have tested the step by step procedures in this thread (
LINK) that I created on the F15 forum, on a 2013 X5, and it worked flawlessly.
I have been driving a '13 loaner for a month (don't ask) until my next F15 arrives, and can attest to the procedure working. I expanded the original thread's USB to over 9,000 songs, in a about dozen playlists in a USB, whilst maintaining song order, avoiding duplicate files, etc. Still, I was able to manually place other songs not in a playlist by just dropping them in the USB music folder, for instance, entire albums.
With as many songs as I had, it took two hours to read the USB the first time. At times, it stopped reading, and resume later. Eventually, the entire library of files and the M3U playlists that tell the system about the structure of playlists were all loaded and maintained as specified. Subsequent shut off and restart did not produce any delay in reading the library -nearly instantaneous.
The USB I used was a 64GB one, which means you can far exceed the built-in memory, and have more flexibility in setting up playlists and managing your in-car music. I am happy to answer questions in the linked thread so that the entire body of information exchange remains consolidated.