Stupidly enough, if you read their warranty policy, they got around the fact that it's not legal for a warranty company to remove a warranty for modding the equipment, by forcing you to have a subscription in order to use the warranty. Their website states

The Pod is a product designed to be slept on every night – and designed to last. We stand behind our product with a 2-year limited warranty, meaning if you have any issues or problems, our team will replace your Pod device as long as you purchased directly through Eight Sleep and have an active membership.

Since this membership is the same thing that is connected to controlling the bed through the app from what I understand, it sounds like even if you did mod it you would still be stuck with that remote solution due to the fact that if you canceled your subscription you wouldn't have a warranty, inviting a warranty on a at minimum $2,500 bed is just no bueno

This is definitely a device that I would be putting my States warranty law into effect, because this sort of shit ain't legal in my state

It's gotta be what, a thermostat, a peristaltic pump and a heater/heat exchanger? Replace the brains with an arduino or a pi and a couple of relays.