Maybe I'm over-thinking this, but it would be nice to be explicit for the future.

• A while back we changed the configuration-file to support per-feed options.
  • When we run we'll upgrade in-place, if we need to, for compatibility.
• 82 boltdb #85 will change the format of our seen/state markers.
  • In the past we had flat files, now we use a Key=Value database.
  • Once again we migrate in-place.

The current release is release-2.5, the next release release-2.6 will have the BoltDB changes in it. At some point we're going to drop the migration, and I guess release-3.0 is the place to do it:

• If users upgrade from the latest available release to release-3.0, everything is fine.
• If users skip from release-2.5, or below, to release-3.0 their feeds will be 100% seen as unread/new.
• I guess also we'll drop the configuration upgrade too.

TLDR:

• Next release will be 2.6. It will have the BoltDB changes.
• There will probably be a 2.7, and 2.8 release in the future.
• All backwards-compatibility options will be dropped in release-3.0.
  • Users who upgrade from 2.6/2.7/2.8 will be fine.
  • Users who upgrade to 3.0 from an earlier release will see their emails duplicated.