Subversion considered obsolete

In all version control environments, there's a central location that is where different participants find each other. In distributed systems, this is just a social convention (and subject to change), and not a necessary part of the architecture, and not critical to all operations. In any case, every branch, whether it is the main branch on the official server that the release will be made from or just the representation of the present state on a developer's workstation, could have locks available; it's just that nobody would try getting a lock somewhere other than the interesting branch, which is the de facto central location.