In fact this is the feature i miss in evernote.
I waitied and hesitated more than six months to move from OneNote to Evernote only because Evernote does not have this feature.
But due to OneNotes non-userfirendly mobile app, finally i had to move to Evernote. Since then I have been longing for this feature.
Now, the moment I get this from RELANOTE, I will defintely jump out unless Evernote bring this Sub-Folder features very quickly.