Change 973333 had a related patch set uploaded (by Jdlrobson; author: Seddon):

[mediawiki/extensions/ReadingLists@master] Revert "Reading lists should not be available to IP masked users"

https://gerrit.wikimedia.org/r/973333

Change 973334 had a related patch set uploaded (by Jdlrobson; author: Seddon):

[mediawiki/extensions/ReadingLists@master] Revert "Disallow temporary users from using the APIs"

https://gerrit.wikimedia.org/r/973334

What does the workflow look like for IP masked users?

AIUI the workflow would be the same as for anonymous users: reading lists would be stored locally, and the user would be encouraged to create a (permanent) account so that their lists could be synced.

What happens to a user's reading list when the temporary account expires or the user "logs out"?

The reading list would persist on the device. (This is the current behavior when a user logs out of their account - their reading lists are still present locally). If the user creates an account, their reading list would be synced automatically from the device to the db.

Welcome back :)
My understanding is that will require some changes in the app but not MediaWiki core. Is that correct?

In T351116#9381098, @Jdlrobson wrote:

My understanding is that will require some changes in the app but not MediaWiki core. Is that correct?

Yep, you're correct - all of the above logic will be done on the client side.

Change 973334 abandoned by Jdlrobson:

[mediawiki/extensions/ReadingLists@master] Revert "Disallow temporary users from using the APIs"

Reason:

Per ticket it doesn't sound like this will be needed. Please reach out if I've misunderstood anything.

https://gerrit.wikimedia.org/r/973334

Change #973333 abandoned by Jdlrobson:

[mediawiki/extensions/ReadingLists@master] Revert "Reading lists should not be available to IP masked users"

Reason:

I think this can safely be abandoned? I'm out next week but let's chat in 3 weeks time if not.

https://gerrit.wikimedia.org/r/973333