Is there a consensus among analysts when this will happen? Or is there precedent from previous presidents of when they usually fill open positions in the FTC?
With all of the big headlines in the news recently, this seems to be something that has largely been overlooked by the press. As far as "analyst consensus" goes, I can't seem to find any.
However, there is readily accessible data that you can look at to determine precedent. Also, as of February 10th, 2017, Edith Ramirez's resignation has taken effect. This leaves just two commissioners: Maureen K. Ohlhausen (acting chairman) and Terrell McSweeny (source).
Per this chart, it seems like there have been large gaps where positions have been empty. For example, there were almost two years between Joseph E. Davies leaving office and John Garland Pollard entering (Late 1910s). However, it does seem fairly common to have at least a couple of months between one commissioner leaving and another taking office. But the current situation seems to be extreme. There have been very few points in time where the FTC has been reduced to just two commissioners. If the history of the FTC is taken as an indicator of its future, then new appointments should be expected fairly soon. But to my knowledge, an exact timeline has not been published or agreed upon by the press.