I thought about it, too, but I guess then you really dive into the field of versioning systems and probably it won't be a database system anymore. That is also

I thought about it, too, but I guess then you really dive into the field of versioning systems and probably it won't be a database system anymore. That is also manual conflict handling... I think branching/merging itself wouldn't be that hard to implement, at least if you have a versioned index at the very core (disclaimer: I'm also developing an Open Source temporal storage system). But then you'd have checkouts, handling conflicts...