If I understand this article correctly the problem isn't the missing permission type provided by dropbox but the location of the settings file which was placed on the root level of your dropbox (for historic reasons). There's currently no way to access /dropbox/mythings/morethings/onepasswordfolder and /.onepasswordsettingsfile so they need to get access to / to keep the historic file at root level working.

Disclaimer: I don't know anything about Dropbox permissions or their API, I'm just judging this by reading the article.

Edit: And now that I re-read the parent comment it seems that maybe I misunderstood your comment and it's already possible to have different permissions at different locations.