Not quite the same as walkup sales, but you can now order Apple Watch models for instore pickup.
If you're still keen on getting your hands on an Apple Watch, Apple has expanded the ways it's possible to order one. It's still feasible to order for home delivery, with Apple currently suggesting a 1-3 business day wait for some models. If that doesn't suit, Apple is also opening up store sales for Apple watch, albeit with a catch.
You can't actually rock up to an Apple Store and buy a specific Apple Watch. Instead, there's an online reservation system that then guides you to select a store and a "reservation" time, when an Apple sales person will take you through the sales process. As Gizmodo notes, you also walk away with a slightly different sales bag this way. You can chance your arm by walking into a store and seeing what they've got available, but you're going to end up behind the queue of folks who make their reservations online.