I think ultimately what would be desired is for the site admin to have the option to choose how they want canonicals to be rendered for their site for topics…
Topic canonical URLs
- Render canonical URL for topic and each reply
- Render unique canonical for topic and every 10 replies
- Render one canonical for each topic
I haven’t yet looked at category URLs.
The idea being that yes, this could provide additional SEO advantage over other forum applications.
To truly get the benefit, the TITLE tag should also reflect the canonical so that spiders see the titles as unique.
If each reply can be indexed, then the titles should render like this:
Topic title - Reply 2
Topic title - Reply 3
Topic title - Reply 4
If each 10 replies are indexed, then the titles should render like this:
Topic title - Page 2
Topic title - Page 3
Personally, I would opt for rendering one canonical for each topic, especially since we’re not providing different content material to the spiders. If users want to search in the topic for the specific term they had queried, they can do that once they get to the topic. If Discourse started providing search engines with distinct content per page, then I would change my opinion and go for the pagination approach.
The way things are today, I do believe that the indexing of the individual replies are diluting the SEO potential of the topics.