So in games of Apocalypse, wouldn't it make sense to allow Chaos Daemons (from the Daemon Codex) to deep strike to chaos icons held by Chaos Space Marines? yes they are from a different codex, but it is still a call to the warp, so they can see it all the same.
and to that point, it could be interesting using opponents icons too.... because the daemons would be able to see those too