Using canonical_url is not a new standard, it is merged to steemit in 2019:
https://github.com/steemit/condenser/pull/3435

Support for different frontends for canonical was merged here: https://github.com/steemit/condenser/pull/2995

The foundation of this was laid in 2016 by aaroncox as it can be seen here: https://github.com/steemit/condenser/issues/336

If you'd rather I take this to steemit.com for a discussion, I'm more than happy to start up a post. I figured a simple agreement here though may be easy enough.

I'm proposing a simple change to the way that steemit.com generates it's canonical links, to establish a standard use case of SEO for non-steemit.com websites that are powered by the steem blockchain. The change within this codebase would be simple:

By default on each comment, steemit.com generates the canonical link meta tag as normal. However, if within the json_metadata field the canonical property is set, it will use that value in place of the steemit.com domain.

This would become a best practice for anyone developing a website displaying user generated content from the steem blockchain.

For example, I created a post in with the tag #steemws, titled steem.ws - The public steem api cluster. By default, when viewing the post on steemit.com, the canonical link included into the content would be:

https://steemit.com/steemws/@jesta/steem-ws-the-public-steem-api-cluster

However, if when this post was created, I set the canonical field within json_metadata to http://jesta.us, when viewing the post on steemit.com the canonical link would now be:

http://jesta.us/steemws/@jesta/steem-ws-the-public-steem-api-cluster

This will let content creators specify the origin of their content and control a bit of it's SEO. Bots could also use this to avoid accidentally flagging original content as plagiarism. This concept could also be further expanded to other SEO criteria, but I feel the canonical link is the most important of the bunch, especially with this content technically being available for any website.

I am not asking for steemit.com to allow for the addition or modification of this data, and by default, all canonical links should default to steemit.com. However, if using an external tool (such as a CMS build on steem for running a custom website) I'd expect the tool to automatically append this data to any posts created from that website.

Is this a reasonable request? If so, I'll put forth the effort and issue a pull request.