Are jet aircraft still at risk of hijacking by people wielding melee weapons?
United Airlines Flight 93 history shows that melee weapons are not very efficient: the passengers that are likely to outnumber hijackers at least ten to one can win if they are willing to fight. 

The question remains, how likely is that passengers will go into risks to show the resistance. If it is just about changing the course to land in the different airport, they may choose to be quiet. If they have nothing to lose, I think the hijackers have no chances.