Are they really disabling creation of Nangin?

Yes. You cannot go Nangin for now. They plan to re-enable it further down the road when there are more masters and when the faction points will update as soon as someone changes so people can't take advantage.

You can understand why they disabled it though. Most of the M ranked players want to go to a faction where everyone is M or higher. This means that Sky clan is gonna win all the PvP because Fuj, Jin and Guan aren't going to have nearly as many.