This thread is about the link code, not about the PIN.
PIN: 4 characters, all numbers, for protecting against switching between different users within a Plex Home
Link code: 4 characters (letters and numbers for easily linking “big-screen” plex clients to a particular plex account)
The change was made upon Roku’s request. It is one of the requirements they made mandatory recently-ish, to get a 3rd-party app listed in their app store.
The comment you linked to in the initial post was made by a Plex developer, btw. So that is directly from the horse’s mouth.
