It seems they've disappeared from the product listings, or is it just my shop? I depend on them. I miss them.
Probably the final step of changes discussed here https://www.shapeways.com/forum/t/urls-in-shop-descriptions-not-working.42718 (short links considered evil and somehow not compatible with the newfangled variants)
That is correct. I know there was a reason, I believe with messing with the protection of the private model.
Silly me - given that the ability to generate valid short links at random to access private pages was cited as the reason for their falling out of favor, it would make sense that they only exist when/while the model is public. (Blame lack of coffee)
This is correct. That said, you can still visit http://shpws.me/ and generate a short link with the private key in the URL included should you want to share it that way.