Do you really need to make a case? Does your company not trust devs? Is there people leading that have no idea about technology? SVN is dead. Many devs won't touch it. It's best way to say to new candidates your company is backwards. Many would refuse to work in a company that uses a version control system that has been dead 7 years.
My company still uses SVN, but we have almost 20 years of history in the repository, not including the autogenerated commits from when we migrated from CVS.
My department would like for us to move to git (some sub projects have) but it's important for our process to retain the history and nobody has had the time to figure out if the migration would be clean then update all of our auto-testing infrastructure (which itself is over a decade old) to use git, all while not stopping active development.
You can use a git client to connect to SVN repo, which is really neat if you have to deal with a SVN repo. Therefore I would assume git has no issues with migrating the history from SVN.
It's effort to switch, and we don't benefit from having separate copies of the repo bc we're so small. No one steps on eachother's toes, so distributed version control isn't necessary.
Now, the fact that most devs know git and SVN is dead is not lost on our CTO, but putting the effort to switch over doesn't provide direct value to the customer, so I have to make the case that switching to git would do enough from a productivity and maintenance standard to effect customers.
But just productivity and maintenance but if your devs start to leave or retire, you're not gonna get the best quality replacements for them if you're using outdated tech. No one wants to learn new skills that aren't going to help with their career growth.