Having read the FAQ shortly after my first game last week, this realy astound me:

“Q: Can facedown Xxcha units exist in the same space as an allied units?
A: No. Units can never coexist in the same space as an allied player's units.“

What is the purpose of that FAQ ruling about the Xxcha not being able to coexist face-down with allies ?
There was no real need for it since the rules were clear in my eyes ( „These units are still affected by bombardments and Sol Offensives, but for all other purposes are not considered to be on the game board“ p. 22 and „Facedown units cannot be turned faceup if an allied player’s units are present in the same area“ p. 22) and now the rules on p.22 contradict the FAQ-ruling, without this being addressed in the errata.

Don't get me wrong, I don't want to complain, I just want to know, if there is a balancing reason for this change, before I decide, whether or not to house-rule it back to to the pre-FAQ condition.
Because, this makes things more complicated, and changes the play-style for the Xxcha immensely, since now having face-down units in an enemy’s victory area prevents you from allying with that player, and choosing where to place your face-down units, kind-of can give away your secret winning condition. Its also strange for fluff reasons: being able to coexist with enemy’s but not with an ally ?
So why was that change necessary?

Off the top of my head I'd say it's so an alliance can't "double up" the defense of an area since that could mean up to 40 units for the other alliance(s) to battle in a single space. Clearly a balance issue.

Fnoffen said:

But never both of them in the same round, since the Xxcha units can only be fliped at the beginning of the battle-phase and never if there is an ally present.

True, not in the same round but it's still a huge deterrent. Any units you send into that area will be destroyed either by one force or the other. Unless you're extremley lucky and just happen to have both the leaders played in that specific battle. So why bother? Imagine if Sol allies with Xxcha and, say Letnev. Half of Xxcha and all of Letnev hunkers down on Mecatol Power South and the other half of Xxcha hunkers down with all of Sol on the Imperial Palace. They'll just have to sit tight until round 8 at which point Letnev and Xxcha vacates the premises for a glorious, but very boring victory.

I still don't see it as that much of a defensive boost. They can still do about the same thing by keeping a force within two spaces of the stronghold. The only penalty is that they have to use their move the round after an opponent takes the stronghold, instead of using the move on some earlier round.

Also, I don't think Xxcha would need to leave the area for the victory. Sol just needs no one else to control those strongholds, so if Xxcha is face down alone there, it still counts.

dypaca said:

I've played Dune for years allowing co-existing BG to sit in an ally's space and I've never known it to be a problem. Perhaps nobody I've played with has ever tried to exploit this idea in the way Fnoffen is thinking, but I don't see it as a big deal one way or the other.