For this, I reviewed all comments in T24660: Display the categories on the mobile site for everyone, T152199: Display categories for logged-in users on mobile web stable, and the survey proposal.

Opinions seem somewhat divided. People tend to want categorization in one of the three following ways:

1. Just enable advanced mobile contributions for everyone, which would show categories for everyone just as they are shown on desktop
2. Show the categories under a level-2 heading like content sections (T152199)
3. Have a "Show categories" button (which existed before but was mostly (?) removed with T246049)

Additionally, there is concern of showing too many categories and cluttering the view (which could be solved with #2 and #3 above), as well as separating tracking/organization categories (i.e. en:Category:Pages using the Score extension and commons:Category:CC-BY-SA-3.0) from actual content-related categories like en:Category:New York City and commons:Category:New York City skylines. There was talk of engineering a "likely relevant category sorter", but those who chimed in all seem to agree this is hard, and the rudimentary attempts at it in the past have had issues (T163699). There is little research showing how useful categories really are to readers, but it is clear that the communities prefer categories to be available to all users, not just logged-in users.

On Commons specifically, many have highlighted how important categories are for general navigation. This likely still holds true today, but is less of a problem now that we have Special:MediaSearch (i.e. compare a search for New York City skylines versus browsing the category).

Key recommendations

This represents my recommendations based on the above analysis. We should consult voters on the project talk page asking for more input, as needed.

• Our solution should make categories available to all users, not just logged-in users.
• A "likely relevant category sorter" is going to be very hard and is probably not worth our time. We can, at least, separate out tracking categories if we want to, but "organizational" categories like commons:Category:CC-BY-SA-3.0 are more difficult to ascertain programmatically.
• Simply enabling advanced mobile contributions for everyone is going too far. There is a clear advantage to the lightweight reader-oriented design of MobileFrontend/Minerva, and we should respect that.
• Add/removing categories should be out of scope (there is not even a native solution in MediaWiki for desktop editors)

Conclusion

T152199: Display categories for logged-in users on mobile web stable seems like the easiest path forward and is a nice compromise to the viewpoints we've seen presented thus far. It should, however, be applicable to logged out users too, and we should consider lazy loading categories to avoid loading all that HTML that may never be seen by the user (similar to why navboxes aren't loaded in MobileFrontend). Additionally, it could use level-3 headings to separate tracking categories from other categories, where applicable. Upon deployment, we should have metrics in place showing how often users both expand the "Categories" section on mobile, as well as actually browsing to category pages from the links in that section. This data may influence further refinements to the categories experience.

As of conversation with @MusikAnimal, for product analytics, we could track similarly like for Phonos with statsv. Would we need product analytics support for this or can we figure this out on our own? I'm asking to find out if I need to contact someone in product analytics to prepare for this.

Interesting for context: https://phabricator.wikimedia.org/T211142