We're well into the process of converting the Messaging app included in GrapheneOS into a modern app. We'll be making a new release later today with a completely overhauled user interface written in Android Compose. We've made a massive amount of other improvements and bug fixes beyond that too.
It heavily depends on proprietary Google and carrier infrastructure in practice.
This is the same as practically every carrier feature though. Carriers are a pain to deal with and all their infra is proprietary, so usually only the big companies like Google and Apple have the motivation to integrate with them and build out new services.
This is the same as practically every carrier feature though. Carriers are a pain to deal with and all their infra is proprietary, so usually only the big companies like Google and Apple have the motivation to integrate with them and build out new services.