National Council of State Boards of Nursing only says that starting July 2017 select candidates will receive the research questions. Therefore, I would say that it's up to interpretation as to what that means exactly. It could mean that "select candidates" really means totally at random, or it could mean that the computer decides based on how the candidate does on their test as to whether or not they will receive the additional research questions. I specify additional because I want to be sure anyone who reads this understands that EVERYONE who takes the NCLEX receives 15 research questions within the 1st 75 questions of their test that do not apply towards their score. After the first 75 questions, every question will be a live question that counts toward their score until their test either cuts off, or they get a screen stating from that point forward the questions are all research questions.
In conclusion, you could speculate that only those who do well on the test will receive the research questions and by well I mean if you pass the test. However, it's not clear.