I think Eastern Europe has been 'done' and just doesn't seem as popular as it once was. Been a long time since I've seen anyone I know head East for a stag/hen weekend. It was once a cheap weekend away but that is no longer the case.
I think Wizz could work but mainly on the point of serving people from Eastern Europe to commute to and from home, along with additional tourist from here visiting there.
I think NCL does very well in terms of the amount of destinations. People seem to think it warrants direct flights to literally everywhere with an airstrip, but that simply will not work. As it stands airline ops seem right sized for NCL with good choice of destinations. There are half a dozen network carriers serving NCL with thousands of destinations one stop via their hub if you do want somewhere 'out of the ordinary'.