I have suggested to the devs that they could perhaps store the media library files on the SD cards instead of internal memory to bypass the limit, but I don't know if this is really possible.
The cards are split--as someone noted before, if there were an identically named folder on the two cards at the same path this could lead to bad things if we tried to make the two cards appear as one drive.
The advantage to folder browsing is you can order the files in your own choice of folder structure and potentially be able to browse through your songs more efficiently than the default artist / album / genre categorization. Or your songs may not be tagged properly in the first place but organized by folders, in which case folder browsing may be the only way to go.
If the converse (properly tagged files in jumbled folder order) is your situation, you could use something like mp3tag to put your files into folders automatically according to their tags.
If there is a problem based on internal memory capacity with the number of songs, you are really going to hit a wall very quickly if you have someone load up two 128Gb cards together with an external USB card.
Also are you sure that the FW code can not be written to allow recognition of identical named folders on two separate cards let alone if you also add songs in an identical folder on OTG USB media. The FW ode may for example add a character, either hidden on visible, to the next identical named folder. Folder browsing will be far easier if all music on 2 x cards plus possibly 1 x OTG USB medium can be browsed seamlessly as if one drive. You otherwise are forced up to the root level of the card or USB media.