Next, try to convey the modification to the quantum formalism that I described, whereby fundamental degrees of freedom (such as string-theoretic D0-branes) become entangled in island sets that are disentangled from everything else. (The usual situation is that everything is entangled with everything else, albeit to a vanishingly small degree.)

I don't see why you need to bring in quantum mechanics or D0-branes here. What you're describing is just a standard case of a low-entropy, far-from-equilibrium island, also known as a dissipative system, which includes Benard cells, control systems, hurricanes, and indeed life itself.

They work by using a fuel source (negentropy) to create internal order, far from equilibrium with their environment, and have to continually export enough entropy (disorder) to make up for that which they create inside. While the stabilizing/controlling aspect of them will necessarily be correlated with the external "disturbances", some part of it will be screened off from the environment, and therefore disentangled.

In fact, the angle I've been working is to see if I can come up with a model whereby consciousness arises wherever natural, causal forces align to allow local screening off from the environment (which we know life does anyway) plus a number of other conditions I'm still figuring out.