The article talks about how MTP is used to sidestep the "other OS not supporting filesystem X" issue. But it's not its only use.
MTP's nature allows the "gadget" (smartphone or any linux device) to still have access to the filesystem while it's being shared. The USB Mass storage model is "all or nothing": it forces the gadget to abandon everything it's doing with the partition/fs as soon as it's plugged; and then rescan everything (for safety, database updates, etc.) when unpluggued.
That is a problem that cannot be adressed with a new filesystem.