Then make it an option in the experimental section of the settings.
If an app cannot accept the updated data, if it has even been launched in the new version, the worst that can happen is that it doesn't work. You can still uninstall, or you can clear the data. You can also pop up a warning before downgrading, explaining the possibility of needing to clear the apps data.
It is still an essential feature for many.
Uninstalling and reinstalling is not only inconvenient, it can also change values like the apps id, that can be essential for advanced users.

For me, the app had an update that removed a feature I relied on without replacing it, making it worse as a result. This therefore makes a valid example to the point made above, that people may not enable automatic updates because updates aren't always better, sometimes they make an app worse.