Is Switch still supply constrained or has demand gone low?
Still supply constrained.
North America is probably getting a bit more supply than before. A bigger amount of consoles will be made available during weeks with big releases, so there's some stockpiling going on.
Going off their 45-50k shipments before MK8D release they are stockpiling around 20k/week right now. If ARMS releases with a similar bump as Splatoon testfire and MK8D then they should ship around 80k that week.
Then they will probably drop back down to the 20k+ baseline. That means they will have around 120k stock when ARMS releases, so that leaves ~40k towads Splatoons launch. With another 4 low weeks that means around 160k-170k shipment for Splatoon 2s launch. Maybe 150k on launch and ~70k second week? After that it should hopefully go back up to the 40k+ baseline. I wonder when bumped up production will finally show.