Thank you all for the boost! I may be overthinking this.
There is nothing like this topper in my closet. The closest I can think of is my white denim jacket and my black square cardi. This falls somewhere in between the two in terms of fit (not as relaxed as the black cardi, not as fitted as the white denim), but I *think* it's a bit dressier than either. If I keep, I plan to wear it to a couple graduation ceremonies this spring, an outdoor baby shower, etc.
I'd definitely wear it with my merino dresses, and I hope I can make it work with my wide-leg pants too (see Finds). I have plenty of sleeveless tops (prefer them over t-shirts) -- silk tank, Uniqlo Supima tanks in multiple colours. I have no doubt it will look fine over jeans+tee type outfits. I'd been contemplating trying to find a white cardi for summer wear (when my black one feels too dark), and maybe this is the option I'm looking for.
I'm away from home this weekend, but it sounds like it's worth doing a round of styling try-ons when I get back Monday evening. I've put together a little theoretical capsule in Finds, showing some things from my closet that might coordinate.