And that's the whole crux of this debate...besides the FCX preview window, what apps use the real res? So far I have yet to see any and Adobe has not said what the next update will do as far as that goes either.
This seems to be the case:
1. The new MBP is capable of displaying 2880x1800 unique pixels - be they image pixels, font pixels or gui elements
2. To prevent "legacy" applications from undesirable appearance (e.g. too small text), the default behaviour is that those apps will be rendered to something like 1920x1080, then scaled to 2880x1800
3. I assume that most commercial, actively developed applications will be able to take advantage of the higher resolution shortly
The main issue seems to be that OS rendering is "pixel-centric", not "size-centric". Applications have been rendering their gui elements etc into a frame-buffer where an area of 8x8 pixels was taken to be "large enough to display a readable single letter". When those 8x8 pixels shrink, the assumption fails. The reason for this is obvious: given low-resolution screens and low-performance hardware, you want to let the applications pre-render and pixel-peek all of their elements for optimal performance and looks.
One might hope that in the future, the design would just be "render this vector object into 1 degree of the viewers field of view".
All of this is kind of moot for photographic content. Photos are always scaled anyways, rendering into a higher resolution buffer is just a matter of changing the scaling-factor.