Well, I don't actually know if I'd have a problem with Freeman in the role… But while it might be cliché and boring to have a Martial Arts expert be Asian, Marvel's done a pretty damn decent job with casting the major/main supporting characters in their movies true to their canonical race. Nighy being cast would be majorly problematic in that case (and indicative to the problem in Hollywood that casting skews heavily white and male).
And what's the argument for changing the race of The Ancient One? We have a lack of representation in the Marvel movies on the Asian end (Bautista is the only one with a major role, and yes, I know that AoS is led by an Asian-American and Asian actresses), so I'd just really, really prefer they keep TAO's race intact from the comics, even if it'd be considered stereotypical.
But I don't really think I'd have any issues with Morgan Freeman as TAO.