Flickr has a blog post on how they plan to keep the commons with their new limits on free accounts.
Short version:
1. Flickr Commons partnership with NASA, Smithsonian, etc are staying.
2. All Creative Commons licensed photos uploaded & licensed before Nov. 1 are staying, even on free accounts with more than 1000 photos. (Further uploads will be limited until they either buy a Pro account or drop below 1000)
3. Non-profits can apply for free, unlimited accounts.
https://blog.flickr.net/en/2018/11/07/the-commons-the-past-is-100-part-of-our-future/