They couldn't transmit such a message; the part beyond "the wall" is moving away faster than light: the data would never reach us. From our perspective, their earlier era is "frozen" in time: red-shifted to zero. We cannot receive any "new" signal from them. Therefore, the seeming "faster than light" violation is not really the case. Relativity "fixes" it by mucking around with time.

From a practical perspective, the red-shift horizon is a pretty solid "wall". The Orange Dude would love it. There could be a million Darth Vaders or run-away planet-eating nanobots on the other side, and they can never touch us. Maybe that's a good thing. The Egyption Empire lasted an extra long time largely because it was so hard to invade. It might even be the Anthropic Principle "protecting" us from really dangerous things.

> the part beyond "the wall" is moving away faster than light: the data would never reach us

To nitpick, the wall itself is moving away at about one light-year per year. The photons that are not moving from our perspective because they are receding away from us at the speed of light will soon find themselves in a space where they are again moving towards us.

"we routinely observe galaxies that have, and always have had, superluminal recession velocities" -- Davis & Lineweaver.

Are you sure about that? While there may be a "neutral zone" where that's the case, it's only a small percent of the stuff that's beyond our senses.

Any information that gets to us via some alien friends will have to travel even further than photons from those stars. By the time we got the alien signal, we would have seen photons from those stars already.