Since Iamat it: Coul open borders be changed? I just don´t see the reason for it to affect rev stability negativly ( debatable of course dependent on other civic choices). I could imagine a bonus to enemy spies though.
Open borders with a civ that uses different civic choices to you (free exchange of ideas that your choices would regard as subversive) is a reasonable rationale for this IMO. Ideally the mechanic would be more subtle, and would give instability only if those players you had open borders with DID have 'subversive' (relative to yours) civics. However, that would introduce a layer of extra AI requirements I'd rather not open up right now (but in the future we may be able to introduce such subleties)