Please take a lot at these articles:
How the UAE Tried to Silence a Popular Arab Spring Activist
The problem at the heart of Saudi Arabia's Muslim anti-ISIS coalition - Vox
Saudi Arabia Forms Muslim Antiterror Coalition - WSJ
KSA has been a ally of the British and the US for many decades. Some Muslim conspiracy theorists claim that Britain and then Israel and a part of US leadership is helping the Saudi Royal family to spread Wahhabism to destroy Islam and weaken the Muslim world. Personally, I do not believe this was the intention, but it was an unintended result, which is costing you now. In fact if it was not for these allies, the Saudi Royal family would not have survived till today. So the US and UK are responsible for much of the mess they have created.
My personal opinion, the problem started with British and French breaking up Ottoman empire and "liberating" Arabs and then soon we see these authoritarian regimes that continue till today. I sometimes imagine if the Turks ruled over these areas, would we still have terrorism that we see today. Israel would probably not exist and the oil money would boost the Turkish empire, but terrorism? I think there would be none.
Saudi's I am sure consulted the US before making this announcement. And I would say the US must take the steering wheel behind the scenes to make this thing come true. The West have broken the humpty dumpty, now you guys need to put it back together and place it on the wall. No one else has the resources to take the lead. But the beautiful part is there is no Western ground troops needed for this solution, the 34+10 countries will jump in with all their resources, if the West is behind this effort. And when the time comes, you must let go of some of these characters and families and let people power take over the lead in some of these countries, because without that we will be back to square one again.