If the dev wants to release their app on another app store, they would just export the apk. Pirate app stores that share apks without the dev's permission would

If the dev wants to release their app on another app store, they would just export the apk. Pirate app stores that share apks without the dev's permission would probably need to write their own aab to apk converter and sign the apks with a key owned by the pirate app store. So this probably isn't a big deal for regular devs, but will reduce the security of apks downloaded from pirate app stores since it would be harder to verify the code integrity of the derived apps.