So that automatic upstream version check for svn sources can be performed, same as for git.
Now that all subversion SRC_URIs have been eliminated from oe-core, this is perhaps not particularly pressing.
Is this something we still want to add?
I'd say no. Oe-core has been svn-free for a long time, and there's only a handful of ancient recipes in meta-oe using svn.
Subversion has few if any users in the YP community. If someone wants to work in this, please do so.