In the same manner, the more users use NXT the more users will more likely use NEM too. The more developers experience Ethereum platform the more developers would develop NEM Dapps.
We should be realistic. NEM wouldn't get popular soon. This is a very very long term project. It would take at least 5 years for NEM to gain the attention of its core future users. NEM is building economy for the future not for today.
What I personally like about the NEM project is that it solves almost all the major problems in all previously released cryptos including NXT and BTC, advancing features in all directions, advancing security features, enabling flexibility for future development, very efficient and green for the environment. NEM is indeed a block chain technology innovation with great unlimited potentials.
I generally think in the coming years we will see BTC, NXT, and NEM all adapt and improve, though there is no way on a tech level BTC can ever catch up to NXT and NEM now, and these two will just keep on advancing. As time goes by I can easily imagine each of these getting well defined user bases for different areas. There is no one search engine. People might think "Google" is the only one, but that isn't true at all. There are lots of countries where Google barely has a presence. I feel like blockchains will be like that too. Bitcoin very well might be the blockchain with the biggest user base for quite some time, but that doesn't mean other chains can't specialize and get their loyal and substantial user bases.