Recently it was announced that Jeremy Carver has been tapped to write the pilot script for a new NBC show, "Frequency." It's based on the movie of the same name that came out in 2000. He would also be Executive Producer.
I've gotten some questions asking if this means he's leaving Supernatural. The answer is, not sure. He is only contracted for Supernatural through season ten. He has an overall development deal with Warner Brothers (much like Kripke), so his talents are likely desired with other projects. This does happen with successful show runners with WB. This is only a pilot script. It is not a series pickup or even a pilot pickup. If it does get picked up though, it does seem that Carver will be busy.
CW show runners Julie Plec and Greg Berlanti produce other shows while acting as executive producers of their initial shows. They both stay involved, but have left much of the control their shows in the hands of their lieutenants. For Plec, The Vampire Diaries is run by Caroline Dries and The Originals is run by Michael Narducci. Berlanti has multiple people running both Arrow and The Flash.
The difference in Plec and Berlanti's cases is they were creators of their initial shows. Jeremy Carver doesn't have that attachment to Supernatural and may choose to make a clean break. He might also remain as a Executive Producer while handing over the show daily operation to someone else. Who could that be? Adam Glass is the most senior producer (in title) on the current writing team and is the top candidate. Andrew Dabb might also get offered a co-showrunning role as well, but it's not likely that he would be sole show runner.
There are also rumors that Robert Singer will step down after season ten. If that's true (and that one still remains just a rumor), then that does put the show in a different position. Jeremy Carver could end up taking Singer's role, but he wouldn't be a very active producer if Frequency (or another project) gets picked up. The other candidate is Eric Kripke. He's currently working in that abyss known as "development hell" and a return to Supernatural might be the best option, especially if they have no experienced show runners left to run the show. HOWEVER, if Kripke did return, it could come with a timeline and definitive end date for Supernatural. It doesn't make sense that someone of his stature would come back to Supernatural for an open ended engagement. But hey, stranger things have happened in Hollywood. There is also the possibility they could bring in someone else that has never been involved with the show.
This all remains a TBD, but there has been some speculation going on for a while now, even before this announcement, that some changes were coming behind the scenes at the end of season ten. I'm starting and using this discussion thread as a way to track any new developments. If anyone out there hears any news stories or rumors, please do share! If you have any reactions or who you'd like to see run Supernatural, feel free to comment here as well. I'm testing out this new discussion format and this seems to be the ideal test case!