but why start with the $10, when BOC (sic: you) just did a special released of the same amount. Why not start with the $5..
It's a good question. With the Frontiers we saw the $100 & $50 first due to higher counterfeiting of these "Journey" denominations (it was practical). I think there are many more complex reasons we're seeing the $10 Viola Desmond note of this new series first.
A) the printers just re-tooled (or whatever they do) for the new "150" so they would be ready to take on the new $10 design right after the commemorative note. You can see similar advanced design elements in this one.
B) political motives- the Trudeau government has been very assertive with regards to gender equality and there were a number of complaints when the "Group of 5" women were removed from back of the Journey$50. He announced that we would see a Canadian woman on the front of the next series first.
C) Past historical figures (i.e. Sir John A MacDonald) have become more controversial in terms of their past policies so I believe that is why they wanted to change the $10 first. There is no longer a security threat (high counterfeiting that I'm aware of) so they had the luxury to change whatever denomination they wanted to.