In Europe Apple was forced to allow side loading + alternative app stores. https://support.apple.com/en-gb/117767 Might be possible to do more (like call private apis) when apps don't need to pass app review.
You also still need to pay $100/year developer fee for your app to continue to be side-loadable (otherwise they revoke the notarization), and need to pay the €0.50 "core technology fee" per side-load to apple after a free allowance of side-loads.
I doubt it's going to help pebble since they'll have to pay more for users to side-load the app than to install it from the app store.