Once a version of carvel-dev/kapp with support for preflight checks has been released and carvel-dev/kapp-controller has been updated to use that version, kapp-controller needs to be updated to support configuring the preflight checks provided to kapp via the App CR.
For some additional context as to how kapp-controller configures the flags that can be passed to kapp via the App CR, see carvel-dev/kapp-controller#1381 (comment)