The topic of different sites may overlap. That a site exists is not enough for us to rule part of our topic space as off topic.
The launch of Poker.SE didn't make poker off-topic on BCG, and rightly so, because it doesn't matter. Poker is a card game, and thus questions about poker asked there should stay there; there is indeed a standard network policy to not migrate questions that belong to multiple sites "but more one than another".
Similarly the existence of BCG should not make us close questions about digital copies of card games as off-topic, just like the existence of SFF doesn't make lore questions about mass effect or dead space or skyrim off-topic.
Once you consider the "BCG exception" bogus, there is really no more reason to exclude such questions. Are they about videogames? Are they objective, or at least good subjective? Are they reasonably answered? Those are the questions we should ask ourselves when voting, not "can I make this question somebody else's problem?"
Do we have the right audience for it? We never can guarantee that. You can link the question on their chatroom if you're concerned. Do we close questions about the latest NFL title because there's probably very few people here playing that here? If Minecraft.SE launched, would we give up our right to handle those questions?
No, we wouldn't, because it wouldn't make any sense. It also doesn't make sense to reject questions here about a videogame just because it happens to be Klondike.
Strixvaria came back at me in chat asking me if this question would be okay for us.
Is the four move check mate (1. e4 e5 2.Qf3 Nc6 3.Bc4 Bc5?? 4.Qxf7#) the fastest way to win a game of chess, or is there a quicker way?
The short answer is why the hell not. Let me walk you through the long answer before you stop listening. Consider a chess videogame that comes with achievements. One of them is:
Win a game in the fewest moves possible.
Now take the sample question proposed by Strix, actually asked here and put it the way a videogame player would ask it:
How can I win chess in as little moves as possible? any-chess-videogame-ever
Please help me get the lightning speed achievement.
Now tell him that he'd get a better answer on BCG and close his question. He reasks it there and gets the answer as it was posted on BCG.
There is a quicker checkmate called the Fool's Mate which only takes 2 moves.
The moves that demonstrate the checkmate are: 1. f3 e5 2. g4 Qh4#
If you're like me you're now probably scratching your head. f3? Is that like a cell on the board? What about it? Is the move to just stare blankly at it until my adversary flips the table awarding me automatic victory?
See, there is a fundamental difference between the question as asked by Nathan Taylor and answered by Colin D and the same question as asked here: context, audience and the assumptions under which they're written. The same question here wouldn't use chess notation, but a bunch of pictures. It would maybe explain why it's the fastest in simple terms. The answerer may be a chess master but by recognizing that he's answering a relatively simple chess question to an audience of non chess players he can't assume the readers already know anything more than the very basics.
The question of whether or not we should accept questions about advanced chess theory on the site is purely academic and best dealt with by allowing the question to be open, suggesting that they ask it on BCG then letting it live there likely collecting no answers in the process. If the asker wants to make the jump, it's their choice.
Now I assumed there was a game with this as an achievement earlier to frame the question as a practical problem that you are facing, but I posit that it's silly to consider that a required part of why you'd decide to accept the question. Achievement whoring is as arbitrary a reason as any other to interest you in the answer to a question, it's just one many of us can relate with. We don't retort "Why do you need that achievement anyway?". The motivation shouldn't matter.
That's why I say, hell yes, please give us this question. That's the long answer.