There should be a way Users can take photos of their physical cards and upload into the library, maybe with some other criteria to avoid 6 friends all uploading a black lotus one of them has (hypothetical scenario)
I have an Ur dragon deck I've built and put a lot of time and effort into, it's absurd that I would have to repurchase everything to now have it online. Aren't there card codes that are printed on the cards? I remember a Yu-Gi-Oh game used to use the actual card codes that would then allow you to import your cards into. Yes, it's time consuming but would absolutely be worth it for long time players who have full collections that they're ready to play with.