I find your scenario very plausible. Acanuck said he expects the security/military to cut Mubarak loose, and he may well be correct. I still worry that if the demonstrations falter - people do have to feed their families - Mubarak may find or manufacture an excuse to step back in and, "restore order." I'd be happy to be wrong, of course.

As Hawkeye from M*A*S*H used to say, "Military intelligence is a contradiction in terms." I won't dispute the motives you're putting forth for the agencies in question (I don't know enough to dispute or support it), but I do question their ability to control things as well as you seem to suggest. It might happen the way you say, but if it does, it will be due in part to some luck on their part.

This is a Juan Cole post from yesterday, but I think it addresses the strength of the security forces:

Million-Person Marches and the Army Backs Off

... Some analysts are interpreting these statements as a two-pronged strategy. But I wonder if they do not point to a split in the security forces. Suleiman is from military intelligence, not the regular army. The new prime minister, Ahmad Shafiq, is an officer from the relatively elite and pampered air force (like Mubarak himself).

The statement about not using force on the people came from the regular army, which is made up of a combination of staff officers and thousands of conscripts. Army chief of staff Lt. Gen. Sami Anan (Enan) may have decided to preserve the unity of his branch of the armed forces, the closest to the people, by throwing the other three under the bus.
...
Thus, Suleiman’s offer to negotiate is probably a way of trying to keep the newly appointed military cabinet in power, perhaps with an eye to new elections, by reaching out to and perhaps bringing in from the cold at least some of the opposition. Lt. Gen. Anan, in contrast, seems not to care very much whether the Mubarak crew stays in power or not, as long as the institution of the army is safeguarded and law and order can be preserved.

In a mass popular uprising of the sort now ongoing in Egypt, unity of the military and security forces, their backing for the ruler, and willingness to be ruthless, are key to a government remaining in power. This combination of factors was present in Iran in summer-fall, 2009. But the news out of Cairo late Monday and into Tuesday suggests deep divisions and diffidence in the military, which bodes ill for Mubarak.

It's taken a few days of internal debate, but army brass have apparently decided their interest lies in propping up the regime. Troops on the ground were reluctant to clear Tahrir Square of peaceful protestors, so -- no problem -- the Interior Ministry's thugs simply manufactured today's violent clashes. Now the army can shut all demonstrations down while claiming not to take sides. Just restoring order.

Nobody in Cairo will believe it, but that's OK. The blatant charade also serves to tell the anti-regime protesters, "We don't care squat about what you believe, think or want. We're in charge, we have always been in charge, and we'll remain in charge. Suck it." That's also their message to Obama and the rest of the world. They're not even covering their tracks anymore: Those police IDs the Molotov cocktail-throwers were carrying? Must be forged or stolen.

We're running out of time for David's "whiff of grapeshot" theory to kick in. The regime is betting most protesters will finally yield to ingrained fear and fatigue, the diehards can be mopped up, and the reprisals can get under way. Everything depends on what happens tomorrow. If the protesters defiantly march, knowing the regime has taken the gloves off, I think they'll win. Because the Friday morning turnout, after prayers, will be even larger and angrier.

This is the tipping point. When a government makes no bones about beating up Anderson Cooper, it's going all-in. As the French say, "Rien ne va plus." Or as Dylan said, "Don't speak too soon, 'cause the wheel's still in spin."