There's nothing you should get for your MacBook (right now)
In doing my research, I found just two solutions that sort of have what you want. Both also focus on including more I/O, not just the battery. My guess is for a product of this nature, they'll all do this.
At 71.61 Wh–146% of the MacBook 13" built-in battery–this thing packs a pretty hefty punch. However, your wallet will also feel it. Compared to other "dumb" battery banks with similar capacity, it's a hefty price to pay. Sure, you get more I/O and (optionally) storage and a great form factor, but that's a lot of $$$. Note also that, while shaped like the MacBook, it is not a case and does not sit flush with the MacBook, and is much closer to a pad than a case.
Finally, note that this is an Indiegogo project, and so far, doesn't seem to have any reputable reviews or even confirmation of shipments as far as I can tell; it hasn't even finished shipping to backers. There's really no way I can recommend you buy this product at this stage.
It's a beautiful product by a reputable manufacturer that basically does what the Linedock does, but better. Only issue: it really doesn't exist yet. There's no pricing, specs, or even delivery date. While at least one prototype was created, it did not include a battery. You can't preorder it, and there's no way I'd recommend you do.
Random battery banks?
Unfortunately, as far as I could find, there aren't any plain battery banks that are even close to the form factor of a MacBook. Even sites making recommendations specifically for the MacBook at best just end up recommending slim battery banks like this Aukey model, and unless you want to carry one separately rather than affixed to your device, I can't seriously recommend one.