There *was* total German reunification in 1990. Except in 1938-45, Austria has not been part of Germany since 1866.
I agree! The History of Austria is very different from german history, and even though austrians also speak german, their culture is also different. Prussia as an idea was the force behind the german history, the austrian state and culture was shaped by the Austro-hungarian history. I think the two states differ quite a bit, and so it would not be a unification at all.
If at all, I'd propose some kind of Austro-bavarese federation, because Austria and Bavaria have more in common culturally. But I think even this thought experiment might not be possible at all.