I'd suggest that Egypt is more likely the keystone.
Upon a moments reflection, it’s clear that Israel is the keystone of the ME.
I'm no expert. (got that out of the way)
History seems to suggest that many of the ME nations side with the anticipated winners of any conflict. Normally they side with whoever is allied with the US. Iran and Syria are the exceptions. Turkey, Egypt, Pakistan, Saudi Arabia, UAE, Kuwait, etc. They tend to wait to see what everyone else is doing, pick a winner and hope to not get any on themselves.
I fear this situation is more volatile because Moscow is making moves in defense of the Paeos and influencing Egypt. If the ME picks up on the fact that Israel is on her own in this, they may smell blood in the water and throw in.
Iran is loving this. His man got re-elected and the machines are spinning.