There’s not really much you can do to improve the iPhone’s design in the near future. The battery dictates the thickness, the glass back needed for wireless charging dictates the weight, etc. Any design improvements that could occur in the next couple of years would be minor, eg. a smaller notch, reduced camera hump (unlikely with the rumors of triple lens), slightly more bezel thinning, none of which would represent a meaningful change in my opinion.
We are definitely not only a year or two away from having zero bezel and zero notch as some people seem to think. It might become technically possible in that time, but I don’t think it will be replicable at the scale Apple requires until at least 2021. Unfortunately, that’s really the final frontier for the “candy bar” style smartphone unless a different form factor like foldable or transparent phones becomes mainstream.