This Plantronics case isn't that great. You have to open it with two hands in front of you, and carefully place the awkwardly shaped headset in. You probably have to look at it while doing so. It's rather large, and the clear plastic cover looks like it can break pretty easily. It's also only one ear, and it's a $30 accessory.
The AirPods can be opened one-handed while in your pocket, and you can place them in without looking. They're also smaller, the case looks quite a bit more durable, and they work with the charger you already have as an iPhone user (lightning). The AirPods and case were designed with a broader UX scope - the entire user experience, from opening to listening to putting away - as one unified product.
The process that most hardware teams typically take is more narrowly focused on the core product hardware, rather than the entire scope of its use. If Plantronics had designed their headset with a broader UX scope in mind, they probably would have designed the headset itself differently, because its awkwardly shaped and hard to store. Instead I imagine they optimized the headset design for solely when its on-ear, and then asked how they could make a case for that shape. Such are the little differences that distinguish between regular products and category-defining ones (see also: iPod with iTunes).
I've got a pair of Bose QC 35s and though their pairing experience is standard annoying bluetooth pairing, their support of multiple devices/easily switching between them is the best I've seen in bluetooth headphones I've purchased. The AirPods are, apparently, comparable to the Bose in this regard, with a better onboarding experience.
From who? They're not available, not even any pre-release reviews around.
http://www.plantronics.com/us/product/voyager-legend-case
(I know that this product is not specifically music-oriented, but the operation principle is there still).