The tradeoffs will fundamentally be the same. You're not getting a > 100mm^2 sensor (with the glass lens required to image on it) on the iPhone anytime soon (or anytime ever really, unless the form factor of the iPhone dramatically changes).
I don't think we're getting a f/1.78 lens on the telephoto anytime soon. The widest aperture the tele's ever had was a f/2 on the 12 Pro, and that was back when the tele was a 2x (52mm equivalent, so not even really tele...). Maybe f/2.4 or f/2.2 (what the ultra wide has)? That'd already be a significant improvement.
The next big upgrades on the ultrawide/tele for the 19/20 generations will likely be larger sensors - they're currently 1/2.55", compared to 1/1.28" for the wide lens. I don't think they can fit three 1/1.28" sensors in there, so plausibly 1/1.7"? But that might mean that effective aperture remains constant.
(and yet none of that will beat an equivalent focal length lens on your XT3)