The rumor going around during the offseason last year was that there wasn't anyone who was both palatable to the NFL and who actually wanted this job. Blandino resigned in April but it was well known at 345 Park that he was headed out. They promoted Dean during the 2016 offseason to a SVP position to encourage him to stay on with a higher rate of salary, but apparently the NFL execs knew it was a matter of time before he jumped ship to take TV money.
Riveron was hired in May but supposedly the NFL was looking around much longer than the time between Dean's resignation and Riveron's hire. They "settled" for Al. I would not be surprised to see a mutual parting of ways at the end of the season given the tumult that's transpired.
Total speculation, but the leading candidates in my mind for the job would be Bill Vinovich (who has previous experience as a replay official for Hochuli's crew), Bill Carollo (former NFL R and current Big Ten director of officiating), and Walt Anderson (who supervises Big 12 officials in addition to his job as an R in the NFL).