The company has a plan, apparently, but no timeline

Pocket incorrectly stated in the recent Mozilla Support article that the service won’t work on Kobo eReaders following the migration of Pocket accounts to Firefox. Pocket integration is an important offering that Kobo provides eReader users and we will continue maintaining our support through the Firefox transition. The Mozilla team has updated that article, which now includes the proper information. 

Kobo users logged into an existing Pocket account will not be affected. For new Pocket users with accounts created after August 15, an eReader update will be required and Kobo will have a new sign-in flow to support Firefox accounts. Existing users who want to switch to a Firefox account to login must update their eReaders at that time to continue using Pocket.