Samsung Messages is not being pre installed on the new flip and fold phones, at least in the US. I'd venture to say the app will receive a security update once in a while but no new features.
Just because it isn't pre-installed anymore doesn't mean they are getting rid of it my guess is that they are doing this to create less confusion for people by not having 2 Messages Apps installed and the fact that certain carriers like AT&T and TMobile for instance only allow RCS Messaging via Google Messages
