Frame shift: where do you see this both being necessary and to be expected?
a white minority that is doing badly
a government that is well-run and compassionate enough to run ethnically-based affirmative action-like programs?
a government that recognizes race-based criteria in a positive sense
Starting with the last, a number of European states don't allow racial data in official statistics. France is the one I am most familiar with.
Second, I wouldn't expect a dictatorship or some really corrupt country to run this kind of program. So, just to take an example off the top of my head, Zimbabwe is straight out. Japan is well run but not particularly known for going out of its way to support other ethnic groups.
And finishing with the first, from the small list of countries that are left, in most cases whites are either a majority or a somewhat prosperous minority.
If in the future whites do become a significant badly-off minority in some well-run political entities that use affirmative action, well, yes, I would expect the same sense of justice (as well as self-interest not to entrench permanent poor, hence low-tax-value, underclasses) that motivated affirmative action to apply to that white minority.
If it didn't it would undermine the justification for having affirmative action in the first place. Is it about making the country as a whole better off or taking revenge for past misdeeds?
But for now this remains a somewhat hypothetical, if interesting, question.
p.s. Driving everything from guilt isn't super-productive. As a European, white, non-British (French, actually), 1st-gen immigrant to Canada, I am willing to consider the guilt of what was done to indigenous people by the British. After all, most European colonial powers exhibited beastly behaviors in their colonies, so there is a sense of "solidarity" between us.
But Canada is becoming ever more ethnically-mixed. If Europeans become a minority in a province, should you expect say Asian-descent Canadians to take on the tax burden of paying for "white guilt"? Why not vote out those affirmative action programs toward indigenous people? You need a more positive and forward-looking justification for those programs, intended to help people.