Azure
You write, 'My guess is that it will be Hezbollah, not against Israel but against the other Lebanese. That's why Nassrallah has been concentrating his armaments from Syria north of the Litani'. There are a few other reasons why Hezbollah has been fortifying itself north of the Litani: one bit of speculation is that Hezbollah is seeking to create ethnic contiguity between the Bekaa valley and southern Lebanon, to ease the transport of men and weapons from the Syrian border. Right now the only thing standing in the way of this contiguity are Druze and Christian villages in that region, and there are reports of Iranian-funded Shia businessmen buying up real estate in these areas and transferring in Shia. (Don't expect any Amnesty International reports about ethnic cleansing.) Aside from the weapons-smuggling benefits of this project is the reality that Hezbollah's ability to fight from amongst its fellow Shia is vital to its ability to operate as an effective guerrilla force. Hezbollah needs to be able to work and wage jihad from among the Shia. Another reason is UNIFIL, whose purview is limited to the region South of the Litani. Is UNIFIL doing a whole lot to stop weapons smuggling and Hezbollah's rebuilding efforts in the South? Of course not. But one reason, I suspect, we keep hearing about Hezbollah's north-of-the-Litani work and not about its south-of-the-Litani work is because down in UNIFIL-land, Hezbollah is a bit quieter in its endeavors, and also because Hezbollah has made southern Lebanon very sketchy territory for journalists. UNIFIL and Hezbollah have an arrangement worked out in which Hezbollah will not be too conspicuous in violating 1701 and UNIFIL will not be too ambitious in doing its job. I was in southern Lebanon a few months after the war, and already this is what the villagers I interviewed told me to my face.