Buried lede: “What I did find was a "convenient" backdoor that Sleep Number can use to SSH back into the hub (and my internal home network as a result).”
Devil's advocate. As someone who has developed a Linux based appliance with over 100k live units across the globe, it seems insane to NOT have access to the thing you're selling and that you have to maintain. If your thing breaks or gets bricked by an update, you will call support and expect them to fix it. You don't want to send in your device or have a support technician come to your house to fix it. So yes, to the…
Auto-update is de facto isomorphic with remote access capability but that doesn't mean you should have a remote shell. At most, maaaaybe a way for the customer to enable a shell for developer support.
Otherwise, a/b setup to avoid remote bricking, DFU or whatever current standard for customer driven unbricking in exceptional cases. But really, test all the forward and reverse update cases and keep a handful of samples of all shipped hardware so you can make sure everything actually works, and you can figure out how to fix it when you mess it up. Always test upgrades starting from factory fresh with all the versions you ever shipped from the factory. (I've run into products where several updates in, version X would work or not based on the original version from the factory forever ago because of original config or something that didn't get migrated properly but never caused problems until recently).