[lmm]

> Database systems have been able to deal with concurrent updates for quite some time now, so I don't think doing this is technically difficult with the current state of the art.

Traditional ACID systems can't really handle them nicely - your only choice with an update is to commit it or discard it - so you have to do a lot of handwritten logic on top, and even if the database itself handles that well, the layers above it generally don't. Event-sourcing style systems work well but they're still not really mainstream yet.