If you haven’t already – see this https://thearmoredpatrol.com/2018/10/31/data-new-mission-reward-tank-population-eu/
This is how many folks have completed the respective campaigns in the last month. Keep in mind this data only reflects those players who have played at least one battle in the tank.
Seems like it’s still going, and not a lot of people have obtained these special tanks (yet). You can see the people who own the tanks are also high skill players that are performing well in these tanks.
This data is taken from Wotcharts.Eu as of 12/1/2018.