Personally, I am very much not on board with RCS at all. But if I had to choose between RCS SMS and anything by Facebook et al, I'd learn to tolerate RCS.

Because of a lack of end-to-end encryption? I'm still trying to wrap my head around it, but it uses TLS, so I'm not sure of the differences.

The difference is that with e2e encryption the carriers don't see your plaintext, while they do with TLS since they terminate the TLS connection on their end.

If RCS is a standard what's stopping someone from writing an app that encrypts your plaintext? Sure, it'll leak meta data, but at least the actual plaintext is encrypted.

Nothing, but you need all your contacts to use a compatible client. I really hope something like https://messaginglayersecurity.rocks/ takes off and that we end up with good e2e interop without having to rely on a single vendor.

Couldn’t you just do the same thing with sms today?

Already done ~10 years ago, it was TextSecure, the predecessor to Signal.

https://en.wikipedia.org/wiki/TextSecure

No, because of the added complexity and the introduction of the need to be more on-guard about it (because of things like addressbook discoverability and so forth). One of the main things that I like about SMS is that it's a simple, no-nonsense text-based service. If it were to resemble the various chat services that are out there, it would make it less useful and appealing to me.

However, as I said, this wouldn't be a dealbreaker. I wouldn't like using it as much, but it would still be better than nothing.

Don't forget "universal". Everyone has SMS, so it's the fallback to everything else.

Also, it works without a data connection.

The longest lived and most used services are always federated and have open standards, like SMS and email. Like you say, everyone has SMS and everyone has email, so they're the defacto standards for communicating with people you're not quite familiar with.

This is why FB chat, whatsapp, etc will never gain the traction that these services do -- putting time and effort into making them work is just a fool's errand until they open up the network to third party clients and make the specs an open standard.

Will Apple actually implement RCS though? iMessage is a selling point for iPhones.

If Apple added RCS support into iMessage, I'm guessing it wouldn't hurt their sales too much.

Exactly. There should not be a reason I can see that they can't incorporate it like they've done with SMS.

Is it though?

Yes.

What are key differences of RCS from MMS?

This covers it pretty well: https://en.wikipedia.org/wiki/Rich_Communication_Services