I see 3 major problems with NXT to become a major payment network.

1> Its distribution to 73 big stakeholders through an IPO.

It will be difficult to justify, a lot of people find this outrageous.
It's already difficult for Bitcoin (62% of survey respondents think bitcoin is a scam).

2> POS system.

Miners are important parameters in the ecosystem and marketing.
Investors are important to miners and miners are important to investors.
Both Bitcoin and Litecoin had a huge amount of miners on-board before anyone started using it in markets.

3> JAVA

Probably the worst.
Java is considered bad by many developers. Java is trying to install a shitty toolbar every time you install it or update and it is so insecure.
No open source programmer would ever use it.
Many people don't like Java and they will never add it (I believe it's why mcxnow never added it because it's Java client).
C/C++ are languages of choice of the industry. A C++ client should be developped to become something “professional and credible”.