That sounds useful, but not as useful as transactions on joins.

It's great to have transactions when you have to cross reference data, on a key/value store, although you can have range queries I submit that kind of operations is less frequent.

But still, it sure is great to be able to run a batch of operations with the confidence it will be transactional, I'm sure there are many use cases that can benefit from it.

Oddly enough, it's strange that there aren't more NoSQL engines offering this feature as once you have MVCC you've done the hard part and AFAIK several NoSQL db have MVCC.