Time to get that OLED screen eh?

Yep. Had been holding off cause I was waiting to see if there would be a new Switch in the near future, but I was weak. 

I wonder if the 60/40 split of Xbox SX vs SS is unique to Japan or is indicative of the worldwide split?

To me it looks like a crapload of people wanted a Zelda themed Switch.  (I mean BotW was the series that originally launched the system.)  So, for several months now a good amount of people have been waiting, holding out for the Zelda OLED, and now it is selling as fast as they can put them on the shelves.  If there were no Zelda OLED, then I think baseline would have been a few thousand higher each each week, but what actually happened is they waited for the Zelda OLED.

That is what it looks like to me.

Usually themed hardware only boosts sales at the beginning, cuz the people that wants it would most likely be massive fans buying it day one. Like even Splatoon and Pokemon edition didn't impact hardware sales this much if my memory serves me correct, and those games are much bigger in Japan. We are forgetting about the Mario movie tho. I doubt it had the same effect as Zelda for Switch sales, but maybe it had a slight impact WW. Games like Mario Kart and other Mario games ranked high physically and digitally than usual. 

I also want to mention the increased sales for Botw. We saw Botw ranking high physically and digitally in multiple regions. So maybe that proves that there are new people trying to ride the Zelda hype train, hence the boost in hardware sales.

I don't think the Zelda OLED primarily accounts for the hardware boost this long after its release.
I feel like it's more likely that the TOTK hype train managed to get some folks on board that hadn't boarded the Switch train yet, and pushed others to finally upgrade their older models.