About don't write sitemap to the disk is a good idea, i love it. Thinking about big sites, add the file to the cache is the way to go... because query can be simple, but big sites can output easily more than 5 MB of data with a sitemap.
The feature that i miss a lot is have more control over parts of the board added to the sitemap (users, discussions and tags). Will be nice have a an option to include/exclude these three parts of the forum. Imagine that i decide not index tags, at this momet the plugin is limited because if i added a
robots.txt to not allow indexing tags but i'm sending a sitemap that contain tag's urls, this is a confusing signal to the search engines.
Also be able to setup the "changefreq" and "priority" parameters according to the forum part will be great.
Also observed that:
- On title changes the lastmod is not changed ❌
- On reply added the lastmod is changed ✅
- On edit contents of a post into discussion, the lastmod is not changed ❌
The Google's behavior with sitemaps bigger than 50k urls or 10MB is simply don't process them.
Hope that post this here also works instead go to GitHub 😄