Yeah, I'm sticking with it. I expect reviews to not be very nice to splatoon which will hurt its legs. It will sell more opening week and more than w101 in the long run, but not by much.
It will sell triple that number in Japan alone FW, as the game is currently outpacing Xenoblade Chronicles X (which sold 85k FW) on COMG and doing on par with Pikmin 3 (which sold about 100k FW).
I get that you're a bit pessimistic about its sales, but declaring that it'll sell Wonderful 101 numbers FW is just as outlandish as claiming it'll sell 1m in a month. I wouldn't be surprised if Splatoon comes close to outselling Wonderful 101's current LT in its first week.