The official 4 month review period is the calendar days the FDA...

The official 4 month review period is the calendar days the FDA can use up reviewing the file. When they send a request for additional information(AI) to the company, the clock stops and will restart from where it left off when the company submits a complete response.

So it looks like they filed the de novo application around early December (after getting knocked back on the 510k approach). They then received a request for additional information sometime between (Dec and April). My guess would be January. The first response from FDA is normally 4-6 weeks. The company said they would send the response by end of June, so the clock would restart from then. This leaves approximately 2.5 - 3 months the FDA can still hold up the approval. An extra AI request could stop the clock again. So CY2016Q4 is probably realistic. Here is an excellent article on the current de novo process if anyone is interested:

http://www.meddeviceonline.com/doc/the-de-novo-classification-process-a-work-in-progress-0001

@tyremen, I'm hoping their competitors will need to go through the full de novo process, rather than a simpler "me too" 510k application. See quote from article:

"Review of the entire history of the de novo process suggests that the likelihood of a competitor following a de novo submission with a traditional 510(k) is relatively low, although legally permissible.  Of the nearly 70 de novo submissions cleared since the beginning of 2012, less than a dozen have been followed by a competitor clearance in a traditional 510(k). "