I don't really think about porting to Linux.
As for Mac:
http://en.wikipedia.org/wiki/Xcode
from what it says it supports both C++ and Objective-C
so I hope there won't be any problems with that.
X360 it is similar to PC, it also uses DX9 (SM3.0+)
but it has some downsides:
-it has big-endian cpu (not little endian like all PC's)
-has only 512 MB total ram (averagely giving you 256 for gpu and cpu, this is small amount)
-no support for custom sound codecs (no OGG)
-and what was mentioned before, in 1-2 years possibly it will start dying, because new consoles will appear
Mac's will still be available and with newer GPU's