Watching the legislation being passed won’t be anywhere near as interesting as watching Apple’s response to it.
I have mentioned this before, and I believe the main challenge the EU faces is in wording this set of laws in manner that doesn’t allow Apple any room to wriggle out of them, the same way Apple is trying to have their cake and eat it too with the other Netherlands lawsuit (where developers using third party payments still have to pay Apple a cut, on top of allowing Apple to audit their books).
For one, I imagine Apple would have sideloading turned off by default, and make the feature pretty hidden, to the point where only a small number of users actually bother with it.
They could also make the process pretty onerous and inconvenient for the end user, from maybe requiring a backup of their device, to voiding warranty, to disabling iCloud features like wallet and Apple Pay, to peppering them with various notifications of possible security and privacy implications.
Might we even see a forked version of iOS just for the EU?
It shouldn’t be too hard to frame this as protecting the user’s privacy and security, since their device is now effectively jailbroken and is presumably no longer as secure as before.
Either way, your move, Apple.
