Superluminal communication breaks causality regardless of whether mass is involved, and we have no evidence that effects can happen before they are caused.

Fair point. Another argument in favor of multiple one-ness is that of monocultures. In general things that become a monoculture are more vulnerable to sudden death. For long term survival diversity is good, and I imagine that planet-level conciousnesses would spawn daughter conciousnesses as they expand to other planets. Those daughter conciousnesses would further evolve and reproduce rather than being strongly tied to the parent.

Photons don't have mass either. Yet they cannot exceed the speed of light.

Are you sure about that? Bits have mass.

The underlying substrate on which bits register has mass but do they?

There are more electrons in your RAM if you set bits to 1.