I have many user having same problem.
In ftp most time you are limited to 1000 files, so you cannot manage using FTP.
Using sftp, it work, but it's damn slow when you update the directory.
So yes, using subfolder cood be a nice feature.
What i can do in my plugin, is to check the current sub-directories and a dropdown, so you can select the right directory for uploads.
In your case for eg. you have the choice tu uplaod to to a subdirectory using a select list :
- - upload in subfolder -
- lensadapter
- straps
- othersubfolder