Why is a mandate though? They started as military remnants from Mariposa. They do not accept recruits and only allow their own children to be members. How then can they be so far reaching? I like the BoS, but they should be nothing more than they were in Fallout 2. Enclave should be dead and gone; they shouldn't have even made an appearance in Fallout 3. Super Mutants shouldn't have even been in Fallout 3. And the existence of Ghouls even in Fallout 2 has been considered a mistake; they shouldn't have existed beyond Fallout 1. At this point it's regrettable, but it is what it is. **Unless you mean BoS as in the MWBoS or Lyons Brotherhood? I have trouble labeling them as BoS.
It was my understanding that the major events of Tactics were considered canon and that the work itself is semi-canon. Unless this has somehow changed in the past year? Is that article you posted considered the now accepted explanation? If they decided to change their minds on that, then sorry that I was misinformed.
I hadn't considered the point about "meta-humans" spreading. That gives me some hope that Bethesda only used them as an introduction method rather than plans of using them in every game.