This does two things:
1. Pushes non-US carriers to adopt eSim ASAP, as they know it's becoming mandatory to use for iPhones going forward, and they don't want iPhone users to not be able to use their networks, given the importance of the iPhone use on their networks.
2. More apps to easily/quickly set-up eSims globally. I've travelled and downloaded local carrier apps in order to buy & set-up an eSim without even having to go to a store, so they exist already – e.g. the US carrier T-Mobile I did back in 2019 in NYC (I'm in UK).
So really, looking at the bigger picture – in the short-term, a year of pain for US users who cannot use the physical options abroad, but in the longterm, eSim adoption becomes the global norm. And you'll either download an app to sign-up for a local esim service or pay for a non-plastic plain piece of card with a code on it to get a local esim service.