For me the big question is how does this end for Saudi Arabia? The confused reports coming out of Riyadh would seem to suggest that indeed Saudi has struck targets inside of Yemen. So what happens when Huthi or tribal fighters retaliate by killing more Saudi troops, do the Saudis then retaliate and strike back again at the Huthis this time deeper into Yemen?
I get the impression that the idea of wading into the muck that is the northern revolt is not something that has been well thought out in Saudi Arabia, which also gets at something else I have been asking for a while: who exactly is running Saudi Arabia's Yemen portfolio? It certainly is not Sultan. And although Muhammad bin Nayif clearly has charge of the AQ section, Saudi Arabia is not the US and is not only focused on al-Qaeda. It has a multi-faceted relationship with Yemen.
My impression is that no one individual is in charge, but that different individuals are taking turns steering the thing with little idea of where they are going besides bouncing from crisis to crisis trying to keep the crazy Yemenis and their problems from flooding across the border.
Now there are early reports of Huthi fighters capturing Saudi soldiers, so how will Saudi respond? By attempting to put more pressure on the Huthis by taking their own captives? Is Saudi confident enough in its ability to identify who is fighting that it is certain it will only capture Huthi fighters and not, say, members of another tribe with branches in Saudi Arabia? The conflict in Sa'dah is a bit like quicksand, the more you move the deeper you get.