GPU is not happening for Corona, it would take an entire re-write of the code (which would mean suspending development of anything else for a year or more), have drawbacks in the final quality, etc. We have always held to that - people would expect GPU to be identical to Corona, and it would not be, and not as suited for what people use Corona for (the ultimate in realism).
Some level of Vantage support is planned for Corona 12, we'll know more as we develop it :) This hopefully will be the solution for those who want some GPU rendering of their scenes.
Scatter is shared between the two, I am not aware of any core differences in functionality (you can let me know which things you mean specifically of course, please do) other than our quick implementation of Edge Trimming which V-Ray improved upon via checkbox when they implemented it later. We've already swapped to checkbox on internal builds, so you'll see it in a daily soon. Overall though, Scatter is Scatter, it's the same core, so there should be no major features different in one implementation than the other.
Infinite Plane would be nice, not sure if there is something about Corona technically that makes this something hard to implement compared to V-Ray. I'll check in with the devs :)