[tbrownaw]

Would this put a limit on how well a quantum computer (or any other large entangled system) can be isolated from its environment (how long it can be kept from decohering)? Or was a similar limit already there and this just describes it differently?

[eigenket]

Probably for some models of quantum computers yes, but there are many different ways to build one and not all will be limited in this way. For example the polarisation degree of freedom of a photon doesn't appear to interact with gravity at all, so that wouldn't be impacted by this.