This is an odd position to have, I think, about Syria now:
Will Israel launch pre-emptive strike against Assad?
Sure, it would have been potentially good to take down Assad. Although I find the argument stronger for America because of Syria's role in killing Americans from Lebanon to Iraq than for Israel--because Assad kept the Israel-Syria border as quiet as the Vermont-New Hampshire border.
Although in part that quiet was because Assad had an active front in Lebanon through Hezbollah. I won't argue Assad was friendly with Israel.
Consider this:
Hezbollah has emerged as a big winner in the turmoil that has swept the Arab world since the uprisings of 2011 that toppled governments in several countries. It has fought in Syria and Iraq, trained other groups in those countries and inspired other forces such as Iran-allied Houthis waging a war in Yemen.
I think it is wrong to praise Hezbollah for building a great "army" that blends guerrilla and conventional warfare. They have a light infantry force that gained experience fighting light infantry.
If Israel has corrected the mistakes they displayed in ground warfare during the 2006 war with Hezbollah, Israel will rip through Hezbollah with a mechanized-airmobile assault well supported with precision fires from the ground and air.
And Hezbollah was bled badly losing over 2,000 killed in their Syria adventure. That's a large casualty toll for such a small "army."
So if Israel is planning a preemptive strike, it will be directed against Hezbollah in Lebanon, as I've long suspected they'd do. Especially considering Hezbollah has experienced maximum damage right now from the Syria multi-war.
And quiet diplomatic support from Saudi Arabia in recognition of joint interests would be nice (and no, Saudi Arabia is hardly about to recognize Israel to get Israel to hit Hezbollah. The Saudis aren't suicidal and it is in Israel's interest to take down Hezbollah).
And consider that Egypt, with the deadly threat of jihadis who have an ally in Gaza, has announced a major effort to destroy the jihadis in Sinai:
Egyptian President Abdel Fattah al-Sisi on Wednesday ordered his military command to use all force necessary to secure the Sinai peninsula within the next three months following a militant attack on a mosque that killed more than 300 people.
If Egypt is in on the anti-Iran effort in Lebanon, Egypt needs to be ready to deal with jihadis fleeing the Israeli onslaught. And recall that to move troops into Sinai above peace treaty levels, Egypt needs Israeli permission.
Yes, if Israel really wrecks the Iranian proxy Hezbollah in Lebanon, Iran will be able to build a new front against Israel in Syria. But then Assad has the old problem of inviting Israeli military attention if attacks against Israel take place across the Syria-Israel border. Assad's regime didn't like it before and they won't like it in the future.
So if Israel is preparing a major offensive, the Syria angle is just a distraction from the real target. You can't hide a big mobilization and the only way to achieve tactical surprise is to have people believe your target is something other than your real target.
I'd look instead at Hezbollah in Lebanon as the target, which could be in the path of a multi-division Israeli raid that lasts weeks or even months to rip out the terror infrastructure of people and physical things in south and east Lebanon.
UPDATE: Israel doesn't want Iran in Syria and Lebanon, but kicking Iran out of Syria would be tough:
Israel must somehow block an Iranian presence from emerging. But if Iran is determined, Israel’s efforts will not be enough. Israel then must decide on a strategy for dealing with a strong Iranian force in both Syria and Lebanon while also avoiding a costly ground war.
Does this mean Israel does nothing effective and instead looks long range to ally with Saudi Arabia and Turkey against Iran?
But Turkey is not reliable as it has shown in the past. And Saudi Arabia is a tenuous ally at best over the long run given Islamist strength in Saudi Arabia.
Israel might avoid a costly ground war by treating an invasion of Lebanon as a giant raid that tears up Hezbollah as much as possible and then pulls back to the border fortifications Israel has built.
If Lebanon's government fills the vacuum in the south after Israel smashes Hezbollah and then withdraws, that's great. But if the Lebanese government can't do that, Israel has bought time while Hezbollah is rebuild at Iran's expense.
Which to me indicates that hitting Hezbollah in Lebanon is the best way to at least restrict the Iran threat to Syria.
And if Assad wins, he'll eventually want Iran out lest his country become a larger version of Lebanon. (And if Assad falls, the Sunni majority won't want Iran there.)
UPDATE: Ideally, this weaponry enables the Lebanese army to take over full sovereignty of southern Lebanon if Israel rips apart Hezbollah with a massive raid:
The arms package aims to give Lebanese troops an edge against Islamic State (IS) fighters and other militants massing in the country’s northeastern border region. It is provided through a train-and-equip fund used to build up foreign militaries that has allowed the United States to continue to arm its Middle East partners even as the Trump administration seeks to curtail foreign military support traditionally handled by the State Department.
It's not actually that much money involved. And it is insufficient to give the Lebanese army an edge over Hezbollah.
Unless Israel rips apart Hezbollah in a giant raid into Lebanon, reaching all the way to Baalbek.