Comment by zamalek

That's not exactly it. Light gets redshifted instead of slowing down, because light will be measured to be the same speed in all frames of reference. So even though we can't actually observe it yet, light traveling towards us still moves at c.

It's a different story entirely for matter. Causal and reachable are two different things.

Regardless, such extreme redshifting would make communication virtually impossible - but maybe the folks at Blargon 5 have that figured out.