Thank you for your suggestions!
1) We may support this in the future, but there are some security concerns.
2) The “Secured Folder” with the “Include Subfolders” does this more or less.
3) The “Key Share” feature with the “Secured Folder” and “Include Subfolders” does this more or less.
4) We do have a reseller program, see https://www.axcrypt.net/resellers/ .