Will FFG ever revisit the multi-faction themes that were featured in the CCG era Eldritch Edition? Back then it apparently resulted in a massive amounts of cost reducers and the infamous Rainbow Deck that was propably the most overpowered deck in the game ever. I have been thinking how this theme could be returned to again without messing up the game balance and i would like to hear what everyone here thinks?

One way would be to actually print cards that belong to multiple factions, but how this would be done i have no idea. This would be something similar to MtG multicoloured cards.

Off-faction Steadfast is also a great way to boost multifaction themes and could easily be expanded further. For example characters that have abilities that reflect two different factions, one being the cards own faction and one for the steadfast faction. Or how about Actions on characters that have a steadfast requirement? You could play the character any time, but would get full use from it, or maybe extra icons, if the steadfast condition was fulfilled.
Here is an example:
-Tainted cop. (Agency)
Cost: 3
Skill: 2
Icons: CC
Subtype: Government
Action(Steadfast Cthulhu): Tainted Cop gains an extra T icon and Cultist subtype.

-Psionic mage (Yog)
Cost: 3
Skill: 3
Icons: A
Subtype: Cultist
Action: Exhaust PM to look at the top three cards of your deck and put two of them on the bottom of your deck.
If you have more Hastur resources than Yog, you can target opponents deck with this ability.
(This ability would of course be worded differently)

Before opening this thread, I was expecting it to be about themes like "Cultists" or "Investigators" that tend to span faction boundaries

I guess first off, I wasn't around in the Eldritch days so I'm not really familiar with the Rainbow decks or what kinds of cross-faction cards existed back then.

We've seen a couple of cross-faction Steadfast cards recently I think but it's still a rare thing. I like the idea of having an occasional character that belongs to two factions or can be paid for with resources of two different factions.

Actually, another angle might be a card that can only be used if you have Characters from some minimum number of factions in play - something to help support more viable 3 to possibly 4 faction decks but not necessarily enough to make Rainbow viable. This would maybe also help make some of the rarely-seen cards we have now which can change faction affiliations more useful too.

But, I don't know if I want it to be too common, especially without knowing more about what issues the game has had in the past with this kind of thing.

Here's more to read about the Rainbow Deck, for example: http://boss.sverok.net/CoC/CDA_rainbow2005.html

In the CCG days, 4 turns was usually enough to win all 3 stories - the trick was to get it down to 3 or 2 if you wanted to win tournaments. Very little engagement with the theme and feel - just maximizing card play to win as quickly as possible. Rush decks were too slow, for example.

Yep, that's the infamous rainbow deck.....

What i would like to see is an expansion cycle, where about half of the cards, or maybe even 3/4 are pro-multifaction and some maybe even anti-multifaction, rest the usual stuff. That way we would have a toolbox for 3 or maybe even 4 faction decks and elements that support diversity, if anyone wants to build something like that, but it would not steer the game too far into that direction overall. Actually that is also one point i have been thinking considering card development. AP cycles that work as a toolbox (not completely of course!) for a specific "genre" of decks (tribal, multifaction, control, etc.) so that we could have more variation with deckbuilding from the basic rush and combo themes the games is constantly gravitating towards. Of course this might not work in reality considering the basic mechanics of the game, but still a nice thought.... ^^