I cannot comment on the future of NP or PA's. I can comment on current general trends, without extrapolating to future directions of either discipline.
NP's can practice independently in most states; other states require some sort of collaboration with a physician, though there is lobbying in these states to allow for more independence. PA's always have to practice under physician oversight, though there is lobbying in many states to change the PA's scope of practice to provide more independence. There are some residencies/fellowships in both. PA's have more flexibility with their post-graduate training, while NP's do not. For example, if a PA wanted post-graduate training in dermatology, then as a first assist in surgery, no problem. If a PMHNP got tired of psych and wanted to do cardiology, he/she would have to go back and get trained in another primary care NP specialty first (FNP, Adult NP, etc).