Switch has been down to about 27k per week in Japan for the last couple weeks. It was holding pretty steady at about 45k per week, and then saw a spike to about 75k with the launch of Mario Kart 8 Deluxe. Not sure if this is the result of a decline in demand, or the supply being even more of an issue. Regardless, its still outselling everything else on a week to week basis. May's NPD will be interested, if Switch is again able to outsell the PS4 and X1, then I think its safe to say the Switch momentum is real, and we shouldn't expect any sort of drastic drop off in sales.
Ultra Street Fighter 2 sold about 16k in Japan in its opening week. Pretty soft start. I'm sure it did much larger numbers in the US and Europe, but I am no longer of the opinion that it can sell a million units. At least not until it reaches bargain bins and is sold for a long time at $20 or less. I also didn't realize that Street Fighter V only sold a little over a million copies, and that's on PS4 with nearly 60 million users. Perhaps Street Fighter has lost its popularity? Regardless, Ultra Street Fighter 2 should prove very profitable for Capcom. The investment had to be very low, and is probably already turning a profit less than a week from launch.
I'm still not sold on ARMs being a console seller, or even a game that draws in the masses, but Splatoon 2 is a lock. That game is going to reinvigorate the Switch with any lost momentum it may have had since launch. In Japan, Splatoon is huge, and it has done well elsewhere, albeit not the phenome that it is in Japan.
The Switch will outsell the Wii U in its first 12 months on sale. It is no longer even in question for myself. The long term prognosis is harder to predict, but early on it seems like the constant flow of excellent first party content sustains the early momentum and it continue to chug along at a great pace. The better Switch does, and without publishers like EA and Activision, the more likely they are to come around and see what makes sense to release on Switch. Software support is building very quickly, and that only make the platform all the more attractive to consumers.