Legal is planning to consult with the community about migrating to the 4.0 version of the CC-by-SA license.
This will be a bit tricky, as content will be under the new license only once it is edited. On the app side, the easiest thing is to look at revision timestamp, and if the timestamp is after a specific "transition" date we will show the 4.0 footer and link.
Additionally the 4.0 version has language variants, so a "nice to have" would be to link to the appropriate language version based on the content language.
No work needed as of now, pending the legal/community discussion.