If the Kingdom of Jerusalem were to be independent, it would be nice to have a special notice of some sort when it gets attacked by Muslims or really, anyone else. Knowing when Christians in the Holy Land are under attack would be rather nice...
the resultant kingdoms should also start out allied with those who participated in the crusade so that they're better defended. I've seen Jerusalem get beat up without anyone helping it survive before, and that's kind of annoying. I realize that's pretty much what happened in real life, but there should be a chance of something else happening.
only problem with that idea is that the only alliance type available is marriage alliance. so at that point it's entirely dependent on the reigning king to be active in perpetration for the counterattack. Jihads give a global message to all players but in the case of regional holy wars i do agree that rulers with the crusader trait should be notified of holy wars against Jerusalem... also concidering their power invasions should also get a global message.. i don't know how many time fati has used an invasion and conquered a place i was depending on staying christian without me noticing for 20 years
EDIT:forgot to add, that i also believe that both Zealots and crusaders should have an increased likely hood to join in defense against Jihads regardless of distance.. within reason of course