What are the effects of the Chrome Web Developer extension hijack?

From the Twitter account you have linked, the author says:

I don’t know for sure yet, but it looks like it may have just been adware being injected. I’m still looking into the possible impact.

You have also asked whatever you should sign out of sessions, revoke keys and change passwords. While I do not have access to the malicious code, and am unable to tell what the code did, I feel pretty confident to suggest that you should end all sessions (to prevent session hijacks), and to change your passwords.

I would say that it is much easier to change passwords than later have to deal with your accounts hacked.

They basically replaced advertisements and gathered Cloudflare credentials.

Proof Point has an article with a thorough analysis about what happened.