This was about "career" tanks taking up another class to complete VA faster, thus, allowing them to return to tanking duties in other content. Not about DPS taking up Tanking.
The content design of 3 tanks, was a direct response the original CT (LotA), which did have 6 tanks. The only thing was, the queues were insane because getting 6 tanks took forever. Just like all other content; SC, WoD and VA having only 3 tanks is directly because of the experience of CT.
Then the question becomes, where is the "magic" number? 4 tanks, 5 tanks? We already know, 6 tanks will awful. And, 3 tanks, means tanks now have to wait like DPS have been forced to for years.
