iBanjo talks about hgsubversion which seems to be a good mercurial-subversion bridge at last.
I’m surprised it took this long to show up but I guess the Mercurial community had not prioritized ‘Build a better git-svn’ as something someone should roll out… until now.
Installation still looks a little painful (and requires lots subversion 1.5 libraries) but I am optimistic this will start gaining traction for those that need to integrate with a subversion world.