if you use spring you can still use same approach, read process definitions from file system. There is no hard requirement to use kjars as deployable units though it's recommended as it provides lots of features and is the most flexible deployment strategy when it comes to business assets (processes rules, etc).
So by upgrading libraries and apis you should be able to run your application in pretty much same fashion.
I am using file system for storing Process definition and will continue with the same after 6.1 upgrade. So I dont need any migration for that. right ?