Most people use the term self-hosting (or self-hostable) instead of ejectable.
You can always start with the cloud version and then transfer to self-hosted if you change your mind and continue right where you left off. Not just that, you can also move from self-hosted back to cloud. That makes it easier to get start with a service because you're free to change your mind without lock-in or risk of painful migrations.
As software updates, the shape of data changes. This would make a significantly harder problem to solve.