Do you think he's right that a two-state solution is no longer possible?
Yes, I do. My main doubt is whether it ever was.
It seems to provoke and emphasize a dilemma that has been very much a difficult challenge to the people of the area.
On the one hand, it would present the social and political reality of the area as two very different groups (which I will name "Israeli" and "Palestinians" out of pragmatism, not accuracy) with significantly different rights, expectations and political structures which are supposed to be acknowledged as a direct result of that arbitrary classification. Not just present it as such, but demand that people lend that model prestige as well - by force of law and military, no less.
At the same time, it would also demand both groups to exercise restraint and mutual respect towards each other. Even as it makes a point of reminding them continuously of how many and how deep reasons they have to be resentful of the archetypical perceptions of each other as embodied by those two states.
Far as I can see, that is just not going to work, or even to help.
Incidentally, going on a tangent, many of those same reasons also apply to the Muslim and Hindu populations of India and Pakistan, and reinforce my opinion that Partition was a grave mistake.
If a two-state solution is no longer possible, what becomes of Israel? What becomes of the Palestinians?
Israel can aim for no better than a perpetual situation of besiege as long as it insists on defining itself as a sovereign state, just barely not officially Jewish, in an area that is by any reasonable expectation bound to be surrounded by hostile people in the foreseeable future.
It has to pick two out of three. Military sovereignity, moral integrity, survivability in the long term. I flat out fail to even imagine a scenario where all three can be reconciled.
The Palestinians are in an even worse situation, apparently. They have no obvious long-term goals or political planning worth of that name.
Even if Israel simply promised to leave in the next few months to Australia or something, meant it, and made good of such a promise, that would only buy them a breather before they ended up engaging in confused mutual conflicts not that dissimilar to so many other situations in the Middle East. They simply give no evidence of knowing any better.