But Landauer's principle is a consequence of the Second Law of Thermodynamics, and the Second Law is not, to the best of our knowledge, a fundamental law. It holds in our universe because of special boundary conditions, but it is entirely possible to construct universes with the same fundamental laws and different boundary conditions so that entropy stops increasing at some point in time and begins decreasing, or where entropy does not exhibit any significant monotonic tendency at all.

What about the Drescher/Barbour argument that the Second Law is an artifact of observers' ability to record time histories? That is, the only states that will contain "memories" (however implemented) of past states are the ones where entropy is higher than in the "remembering" state, because all processes of recording increase entropy.

So even in those thought experiments where you "reverse time" of the chaotic billiards-ball-world back to a low-entropy t = 0 and keep going so that entropy increases in the negative time direction, the observers in that "negative time" state will still regard t = 0 to be in their past. Furthermore, any scenario you could set up where someone is only entangled with stuff that you deliberately decrease the entropy of (by increasing entropy outside the "bubble"), will result in that person thinking that the flow of time was the opposite of what you think.

I don't know how well this arguments meshes with the possibility of such GR solutions.