Sure but I guess thats not the biggest issue, he's getting a high resolution retina display.
That's gotta count for something right? (haven't seen the new display's yet but I guess FCPX would look awesome on it)
If he wan't a real good monitor (not that Apple monitors are bad) for editing he would probably go way over his budget.
The problem with a laptop monitor, no matter how good it is... and I assume that the Retina display is good, is that it isn't necessarily consistent. For editing (video or still images) you need consistency. I could argue that a monitor that holds it's calibration is more important overall quality, once you've reached a certain minimum threshold of quality.
Because a laptop monitor can be dimmed, both by the user directly and by the system automatically as conditions change, it is not that consistent. You work around this by turning the auto-dim feature off, and then always setting the brightness to full. And then you'd have to always work in a similarly light area (the whole point of a laptop being it's mobility).
A few hundred $$ needs to be added to that total above for an external monitor for any serious editing tasks, imho.