http://wiki.ffo.jp/img/975/nm_ll.jpg
A lotto spawn. A longer timed spawn. Anything that makes actually getting to fight the NM a nice surprise.
This doesn't make an items rares.
Defeating anything doesn't mean anything. Everyone can do it. No matter how strong something is everyone will be able to do it after someone figures it out. It doesn't make anything rare.
And how matter how "rare" a drop it is after it's killed just means the same people are going to camp it for a month rather then a week.
And why is this? Because you want everyone to have everything without trying.
And what do you want later on? Missions like we have now that anyone can do? To reach this game's "sky" or "sea" and have NMs with instant repop that drop pop item for harder NMs?
Anyone could access anything XI. There was nothing ever telling anyone if you have to play 6 hours at once to do this.
It should take more than 15 minutes to even see NM. Not get the drop for yourself and everyone else in your party.
It really doesn't matter how "challenging" anything is or how easy it is to get anything. No matter what someone is going to get something before you and be better then you.