This project excites me. And i am from the very beginning really explored and found of OS Native architectures. Exploring native APIs or Windows ( WinAPI ) and for Mac OS ( Objective C ). but overall, regarding the project requirements so narrated on the post i think Qt Framework will do the job quite easily which is again a cross platform framework to develop windowed application. Also, know how to pack it up wisely. I also use to do in-house product development based on WinAPI, MASAM, integrating OpenGL to the app, over mac platform also, shooting with Cocoa framework too. So, having such experience i see this is fairly doable without hassle using Qt Framework, and we will be having way backward compatibility too for both x86 and x64 OS arch.
Frankly, onec the requirements are clear, this job will be then done in very good / short time line.