Yes it's safe to assume. That's a whole additional level of display engineering to make that work. If they had it they would have announced it.
I would not expect this feature any time soon. Apple only adds a feature if it really enhances the experience. It certainly does on the iPad, but the iPhone display is too small to justify frequent use of the stylus. Is someone really going to draw art on a 5.5 or 4.7" screen?