There is that already. Click 'Other locations' in the sidebar and at the bottom of the window you have 'Enter server address...' textbox. Put your sftp:// or sm

There is that already. Click 'Other locations' in the sidebar and at the bottom of the window you have 'Enter server address...' textbox. Put your sftp:// or smb:// url there. Discoverable shares (smb) will be displayed in the window. Vboxsf is not a network redirector as it is in Windows; look for vboxfs mounts in the /media directory.