It is there in the S10 stock camera app's settings, so I'm hoping that it's coming to S9/plus soon as well.
Usually Samsung brings these to other devices later on.
Hopefully sooner rather than later. The space savings are massive. A 734KB HEIC picture (sent from an iPhone) converted to an almost 6MB JPEG via the Samsung Gallery.
I haven't tried it out in the s10, does it lose quality for space?