Rather than expect icons for communion you can expect a fix so that slaves don't do stuff. Not that I can guarantee when this will happen, but it seems more relevant, and I'm not powerful enough to make a communion icon, as the effects are obscure .
Well, slaves don't actually get a bonus to casting, which is good.
I have to admit, I like slaves being able to act (cast or attack) when no masters are using them, but having them act just because they go first doesn't make sense.
It would also be nice to see the master's current path levels.