It’s a great idea and I’m sure people will love to be promoted for World Kindness Day.
Many of us promote each other’s shops/items regularly through Folksy Fridays (where we share up to 7 items from other sellers plus one of our own), or by pinning things we love onto Pinterest boards. I think I’ve seen a couple of people doing full shop promotions on Instagram too. Have a look at the Folksy Promotion board here on the Forum (it’s an old thread but updated every week as people do promotions).
I don’t think anyone has said they would rather their work not be shared - I do avoid anything with a watermark though - as the seller is probably trying to control their images.