A real-life situation I ran into:
3) Take a copy of the data store offline, and later merge it back into the online database
Manually resolving conflicts is fine. The alternative is to rebuild a system on Couchbase/pouchdb, or rewrite on event sourcing, neither of which - when the system otherwise lends itself to RDBMS - is my choice.
Does the OP support merging? I didn’t see that.
0) The most obvious use case is to replace git, because git proper doesn't handle big files very well, let alone bigger than RAM structured data. Mind the fact you might still need an ad-hoc solution for binary data. WT does have a limitation on value size.
1) There is various data science uses cases, like sharing data [0] or A/B testing stuff.
2) Anywhere you need an audit trail .ie you need to look back at previous states, whether it is for debugging purpose or domain logic
versioned datastore is a compromise between event sourcing (pure log) and non-versioned databases.
[0] Collaborative Open Data versioning: A Pragmatic Approach Using Linked Data
[1] https://en.wikipedia.org/wiki/Audit_trail
edit: cosmit.