"Not only altcoins, all cryptocurrencies should learn about this. It could happen to Bitcoin, too, in any way. It even happend already back in 2010 when a hard fork was conducted because there was a bug resulting in unlimited Bitcoin creation."

This is the type of thing that worries me most about crypto land and open source in general.  While NEM has what appears to be a great partnership with Mijin and Dragonfly, my hope is that NEM is always aware of, and approves of the features and implementations that these projects expose in the wild. This is especially important because this is a publicly acknowledged relationship, and any failures will have the NEM chain at it's root.  On the other hand, any hack can poorly implement (or intentionally poorly implement) the NEM chain to cast doubts on the platform.  I understand that these relationships are necessary for growth and wide spread adoption.  I just wish there was more controls in place that could protect the hard work that this dev team has accomplished.