The issue with canonical IMO is that app canot change the link. If busy.org change his url scheme or busy.org become busy.com, we would still have old style canonical url from others apps. I would rather recommend 3p apps to use only app.
For the standard that's something we can do at Steemit Inc. We can imagine a repo with all standards. Similar than what was proposed with SteemScript https://github.com/busyorg/steemscript. With that in place, 3p apps would have the possibility to PR change on the repo to update url scheme for example.
Busy is the dopest, words count and easy use makes it an ideal place to use steemit for me...Am your new biggest FAN!
The common solution when a website changes its url scheme, is to setup http redirects. So the work stays in the hands of the website owner to maintain their list of redirects.
This solution currently suffices, because search engines then update their index entries with the new url they got from the redirection, but I can see this solution not being prefect in the long term, since the canonical link entries in the blockchain can't get updated after a certain time. So either the website owner forever has to maintain an ever growing redirection table, or you just let the links break.
I commented above with a possible set of solutions..
https://steemit.com/steemdev/@howo/steem-improvement-proposal-canonical-links#@valuproposition/re-jesta-re-howo-steem-improvement-proposal-canonical-links-20180217t054225178z