I searched on the open standards website, particularly the C working group homepage but only found information about C11.
They seem to have regular meetings and discuss
I sent an email to the guy on the WG 14 contact section but I didn't expect to get an answer anytime soon, however, I did.
This is what he replied to me:
the Committee has not discussed starting work on a new revision of the Standard. WG 14 will be meeting in Parma Italy the first part of April, and so far there as not been any proposals for new features that would prompt the revision process.
Thanks,
John Benito - ISO/IEC JTC 1/SC 22/WG 14 Convener
So I guess this is as official as it gets for now.
It appears there is discussion about the next C standard, C2x, and there are proposals as well.
You can view the charter here.
And, you can view the email list here.
At the bottom of the charter, it indicates an expected publication date of 2022.
There is C18 (https://www.iso.org/standard/74528.html) standard released in June 2018 but it only addressed flaws in C11 without introducing new language features.
A technical corrigendum is issued to correct a technical error or ambiguity. New features and extensions need to be published as an amendment or revision of the standard.
See here for an in depth description of the procedure for developing an international standard: http://isotc.iso.org/livelink/livelink?func=ll&objId=4230452&objAction=browse&sort=subtype