We should create the tag synonym for google-webmaster-tools as soon as possible with google-search-console being the new preferred name as it matches the new official name.
Once the tag synonym is created, no further action needs to be taken. All questions will have effectively be re-tagged to "google-search-console". When users type "google-webmaster-...
Finally, a no-brainer :-) Good catch! It's renamed now.
Here's a discussion about how to rename a tag on Stack Exchange's Meta site. It requires a moderator to do, so you did the right thing by opening up a Meta discussion about it.
It is time to make the change. google-search-console should now be the canonical tag.
One of the criteria brought up last time was which is used more.
"search console" 50 uses since November 30th.
"webmaster tools" 50 uses since October 27th.
In other words, "search console" is used in questions about 25 times per month and "webmaster tools" is used ...
rel-canonical is a specific type of canonical implementation. It uses a meta tag. The other implementation for canonical URLs is 301 redirects. I'd keep rel-canonical separate from the others. I have written a tag wiki for rel-canonical.
canonical and canonical-url are probably similar enough to merge on this site. There could be canonical things ...