Android Q may allow for apps to more easily support Rich Communications Services, or RCS, messaging. A new set of RCS-specific APIs are being opened up for a future Android release, likely Android Q, as noted by Android Police. These changes include a new CTS package as well as renaming and revealing some existing APIs.
Things with Android Q are still early, but it's speculated that if these changes are integrated into Android, any messaging app whose developer is willing to work to adopt these changes could support RCS. Google's Messages app currently supports RCS, as does Samsung's own messaging app, but there are a lot of popular third-party messaging apps out there, and it'd be big if their users could get access to RCS as well.
RCS support in the U.S. is still spotty thanks to the carriers, as not every single operator supports the RCS standard. If Android Q gains these RCS APIs to make it easier for third-party apps to support RCS, though, it could be big for getting more people to use RCS and the features that it offers.
Have you ever used RCS messaging?