Awesome power move by emperor Manuel there. Given his current dominance over the crusader state, the new archbishop already so clearly showing his biases and the Duke of Galilee needing money to ransom his son, if the crusade against Egypt is successful here, I can see the Rhomanoi taking a major chunk of Egypt for themselves. Perhaps the Nile itself will be the border between direct Roman vassals and crusader-held lands, with the bulk of the delta also in Greek hands?
The argument that it's too far from Constantinople does not make that much sense to me - if the Rhomans have a decent navy and no ongoing conflict with a major naval power capable of contesting their presence in the eastern Med, they should have a pretty decent link to Egypt. They controlled it for a long time back in the day, after all.