Multiverses as a result of space receding faster than speed of light are pretty much universally accepted. Other kinds are more controversial. There are galaxies not co-existant with us in the future that are now.
Ahh, I see, we were talking about different concepts of the multivese then. I'd consider your definition of multiverses still as part of our own universe, just not our observable universe. But I think this is more a question of definition...
For the existence and coexistence they amount to the same. There are galaxies now that will leave our co-existance in the future and still exist. Disproves that existence implies co-existence.
