Does this put more arms, well trained troops and financial assets in terrorist hands? (bad) Does it pose a threat to Saudi Arabia? (couldn’t happen to more deserving rulers)
“Does it pose a threat to Saudi Arabia?”
Big time.
Seizing the Saudi oil fields and Mecca are strategic goals of the Iranians.
The Saudi oil fields and oil infrastructure are concentrated in the Eastern Province, which has long had a large native Shia population.
With Yemen, Iran can land shiploads of heavy weapons on the Arabian Peninsula. They can mass an army, and smuggle arms and explosives into the Kingdom.
If they have the combined oil of Iran, Iraq and Saudi Arabia; they will control oil prices for the world, and be fabulously resourced to expand. Coupled with nuclear weapons, they will become a much greater threat than Saddam threatened to become by seizing Kuwait and massing by the Saudi border.
The army that saved Saudi Arabia from Saddam has been dismantled. The heavy US VII Corps which swung around wide and crushed the Iraqi Republican Guards no longer exists - inactivated, and colors cased.
If the Saudis invite the Turks in, Erdogan is unlikely to leave. Egypt has a thousand tanks, and might be able to muster a few hundred operational.