Don't believe JR will start anytime soon.
My logic is based on how MDA tends to motivate his players. First, he tells players what they need to work on. Then he withholds playing time, and or in this case, the right to start, until problem has been corrected. (I am sure there are some things that MDA wants JR to change.)
He simply won't give up his leverage on JR, by continuing to start Landry Fields. In addition, I don't think it is reasonable to assume that Landry Fields will not be able to start shooting a higher percentage from the 3 point line again. I am sure Landry knows what his problem is, and he is working very hard on improving this part of his game. Landry Fields is a bit like David Lee. They both will continue to tinker with their games, and keep trying to get better over time imo.