Inventor's (not Fushion's) graphics uses Microsoft's DirectX (or D3D), not OpenGL. There's also some C# code in Inventor (you'll notice it requires .NET when installing). DirectX is not available on OS X natively, AFAIK. C# on OS X via Mono, perhaps. So I suspect it will require a mammoth effort on ADSK's part to port Inventor to OS X. I'd be very surprised if it ever happens, but I reckon you'll see a huge number of people dumping SolidWorks and Edge for Inventor if they could work on a Mac natively.
But then ADSK did port AutoCAD to OS X, so you never know...
Maybe there's a plan with Fusion, who knows?
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