The question is how big can the calender get, we have places like Mexico, Russia, a 2nd pssoible a 3rd GP in the US. Will the teams allow it to go beyond 20 races and if not which races will get dropped?
I think they would; in F1 money tends to do the talking. More races would mean more money (from TV deals, sponsors, winnings, etc). Obviously it would need negotiating but I think they'd eventually go for it. The problem would be finding time to adequately develop & test the cars so every weekend doesn't become just a race of attrition due to unreliability.
If they did start dropping races instead, some of the European races would be under threat. Hungary would probably be top of the list, I'm guessing.