There are several changes planned which will need to bump database major schema version. Although we have support for profile per channel, a backward incompatible change would be still painful in some situations like using a previous Nightly and then going back to latest one.
Normally, downgrades are hard to implement, but we implemented database shadowing to support seamless switching between old and new local storage implementation, so we can just remove all new databases, including the local storage archive and start from scratch by copying webappsstore.sqlite to storage/ls-archive.sqlite.
New local storage databases will be migrated lazily again using schema current for given build.
This would work until we disable database shadowing. Database shadowing will be disabled once we are confident about new local storage and when all planned major schema changes are done.
At the same time we can also support local storage archive upgrades which can be used for forcing database re-creation, to really fix bug 1542104. data.sqlite for slack.com can still contain invalid usage in the database table (usage column) and the usage file can also be invalid.