> I don't get why you would regulate such a thing.
Because there's absolutely no downside to telling Apple it can't artificially make its iMessage platform restricted to Apple devices. We literally have seen leaked emails where Apple deliberately does this as an anti-consumer platform lock in play. The slippery slope hypothetical you provide is not the reality. Nobody is asking governments to regulate adding cool new features to the and force everyone to comply and implement them. What regulators are saying is that Apple can't deliberately make Sneetches out of us and needs to allow interoperability on their human-critical messaging platform. In the US the DMCA actually makes it explicitly legal to reverse engineer a protocol for the purpose of interoperability. This idea basically extends that to "and you can't punish users for building applications that interoperating with it" but of course is framed as "just fucking stop disallowing it greedy asshats".
If I could install a 3rd party SMS app on iPhone (like how Signal used to work on Android) I'd be more skeptical about needing this regulation.
If Apple wasn't doing this artificially and iMessage actually had features that were innovative, and that other people couldn't reasonably be expected to implement in a way that wouldn't be a detriment to the protocol, I'd be more skeptical. (TBH they've probably spent more resources on preventing interoperability than if they didn't care and let it be open...)
> Isn't this going to kill features that only some apps have or offer?
No, degrade gracefully. If the feature is an improvement for everyone and should be required, we know how to have working groups update a spec and have implementers follow (even when one leads the pack and drives the spec changes in the first place as is often the case these days). If that doesn't work build a new protocol and win people over with your obviously better CoolNewFeature.
It's like you don't believe it's possible with the countless man centuries of resources these companies have to have software both interoperate and degrade gracefully when one client doesn't support all protocol features. I don't buy it; I believe we can.
You're spreading FUD.