Old thread but it seems like the developers thought that "Sync on demand" was just as good as "Selective sync" which might be the reason they've ignored the request. If this is the case, I think a more suitable feature request would be the option to hide notebooks so they only appear when you click a "Hidden notebooks" menu option. This way, when "Sync on demand" is enabled, you don't accidentally see the notes in a search or in your Notebooks list and have Evernote download them. They'd still be in your Evernote account but not downloaded on that computer and not able to be accidentally downloaded. This seems equivalent to the Selective sync feature on Dropbox for example (shown below):
Great suggestion. And if the notebook is hidden it would also be restricted from searches by that client.
Selective Sync of Notebooks per client
in Evernote for Windows Issues (Versions 6.25.1 and under)
Posted
Great suggestion. And if the notebook is hidden it would also be restricted from searches by that client.