“I disagree with the notion that local ferals, even to the extant that they exist, are inherently superior. They demonstrate only the ability to survive unmanaged. Most of their characteristics, small colony size, frequent swarming, strong defense, are not what most beekeepers are looking for.”

Well put. 

“The one huge trait that we all desperately are looking for is the ability to control varroa”
I disagree, the one huge trait we are desperately looking for is to control varroa AND be useful/profitable to us. 

The question is… Is it easier to start with a clean slate, breed positive traits in to wild type bee that has resistance? Or is it easier to select for resistance in a stock that all ready has been selected for other positive traits. 

“So is varroa resistance/tolerance a local issue or a universal one?” 
local, most TF stocks collapse when moved. 
Local adapted stock lasts longer untreated then non adapted stock 
https://www.researchgate.net/publication/262692873_The_influence_of_genetic_origin_and_its_interaction_with_environmental_effects_on_the_survival_of_Apis_Mellifera_L_Colonies_in_Europe

“Will varroa from one area differ from those from somewhere else? I know that there are different strains, but among v. destructor have they adapted to a local environment”
The mites developed different mechanisms of resistance to pyrethroids in the US, UK and Mainland Europe  

“In the long run they should adapt to not kill their host but have we isolated any with that trait?”
balance is not a guarantee, The introduction of house cats has caused the extinction of 63 species, no balance there   

In the forests were hives are a long way apart, maby…
But the way we keep bees favors a strain (both mite and virus)that weakens a hive to the point it is robed and the strain is spread.

As for "locally adapted"  in a program selling bees... Its a marketing buzz word, like mite resistant stock, Sounds good, but its real hard to quantify. 
to me it would mean a fixed operation        

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