The sweet spot for mega-microSD cards seems to be with the Clip+ or Clip Zip with the alternative firmware Rockbox (available at Rockbox.org) on the player. With Rockbox, you get full database capability (with the original SanDisk firmware, the database peters out and refuses to accept more database info. at around 7,000-8,000 files or so on the Clip+ and Clip Zip, and much lower with the Sport and Jam, leaving you to use folder-based navigation); Rockbox also offers many other benefits, including snappy screen designs of various types.
People have reported using a 128GB card in that fashion without any issue, and I believe that I have read similarly as to the use of a 200GB card.
Although the Clip+ and Clip Zip are no longer being manufactured, they still can be found, albeit, typically, at a higher price than the Sport and Jam–but well worth it, it seems to me.
