@smalyshev I've commited work in progress patch that implements SessionUpdateTimestapHandler object before I read your comment.

If we should avoid new object, we may enforce users to use SessionUpdateTimestampHandlerInterface instead. This name might be too long. If you have good name for it, I'll use it. In PHP 5.5, there are SessionHandlerInterface and SessionIdInterface.

I need to get rid of duplicated methods from SessionUpdateTimestampHandlerInterface, but
if we enforce to use it, user save handler would not call bogus base methods that simply do not work. 

I haven't check code in detail yet, it might not work as I wanted, but what do you think about enforcing interface? Preventing bogus method calls seems hard.