It would have been an utter catastrophe. Syria was very much opposed, which made the whole thing problematic from the get-go.
The idea was a straight attempt at a power grab by one branch of the House of Hashem. It was ambitious but doomed to fail. In all probability there would be no where in the world for the House of Hashem to hang its hat by 1960. The most probable replacement would be Ba'athist factions in each country. The suitability of the Ba'athists to rule successfully is amply demonstrated by the nightmare regimes in Iraq (pre-2003) and Syria (to this date) where the movement achieved power. As repressive as the Jordanian regimes have been they are positively Scandinavian policy-wise compared to the Ba'ath Parties.