Rebels can still be supported by anyone (Although your success rate might be very low).Diplos as spies is an interesting idea. So now not everyone will be able to incite a revolt or infiltarte administration, but only the ones having the appropriate ideas? Okay, this is gonna be interesting. Fewer annoying sponsored revolts during big wars.
No, they reworked relations.Btw, considering the scarcity of diplomats, will the improvement of relations between countries be the same old tedious process we had in EU1, EU2 and EU3?
Check this dev. diary about it.