You can do it already. But keep in mind that if you want to send regular text messages (SMS), you must do so through a mobile phone provider. The way this is done on a Mac or iPad should be sent (and received) through your iPhone’s mobile carrier. So you need to turn on Settings, Messages, Forwarding text messages on iPhone. Then you can use iCloud to forward messages to and from your other devices via iPhone. Of course, you need an iPhone to do this. And iPhone and other devices must use the same Apple ID.