In general, for a very large old project that has no major problems with SVN, it's easiest to just leave it. Lots of open source projects are still on SVN (some even on CVS...)
Any sccs users out there?
I knew this one was coming. I've been using it for a very long time and it hasn't let me down. I have considered using git but found no compelling reason to migrate.
Same here, I still use svn on my 20 year old projects and haven't felt the need change. I use git for my newer projects but occasionally run into issues that cause me to have to search for a solution.