There's a similar method to get into an Eight Sleep Pod 3 [0]. This requires less extra hardware though since some models come with a MicroSD card that you can modify. The method used in TFA might be a good way to get root on Pods without the card. That being said, I just learned that while Eight Sleep does sign their firmware updates, they also send you the private key used to sign the update in the same package.
Ironically this makes me more likely to buy one. If I can make the smart thing local and/or home assistant controlled, and kill their internet connectivity... I'm thinking that isn't so bad.
Don't get me wrong $2-4k is steep, but if it's a one-time for a decade or so, that's reasonable. But $4k plus you want $25/mo? Just fluff right off.
[0]: https://github.com/bobobo1618/ninesleep