Katamari Damacy Reroll is set to...roll on the Switch eShop on December 7 alongside of a western demo, but you can download said demo right now for free with a Japanese region account. It's even in English!
All you need to do is sign in with your Japan-region account, search for "Katamari," then grab the demo. Bam, you're good to go two weeks early. Why aren't more demos like this, and why isn't it available in every region? Your guess is as good as mine.
It's insanely easy to make a cross-region account: here's our handy guide. Or if you aren't keen on clicking, you can craft an account right here: just click "Japan" for your region. While you're at it I suggest making a UK account as well as that region also hosts demos and different eShop opportunities.