It's always hard, when you love something you're working on, to know the right moment to talk about it to the world. Some fear to see their awesome idea stolen by other developers, some others talk about them too early. There is no perfect moment to start talking about your game but there are few things you should know.
Don't talk too early
When you talk about an upcoming game, and even if your concept is an appealing idea, people will want to play it. They will naturally want to know more about it and will wait for every updates or news you will be able to provide.
People will take your announcement as a promise. Once they know about your game you will have like a debt. You will have to release it.
As you might know the hardest part in game development is not about the idea, it's about changing this idea into a real game. So it might happen that the game you are working on never reaches any gamers. But gamers don't forget and don't forgive. If your game can't be released they won't care because you have promised something fresh and fun, you have promised something new, something for them… not releasing it would be seen as a betrayal.
The most difficult part of all that is you will always meet someone who will talk about what you announced. You can trust me on this, it will hurt your ego and your feelings every time. Oh they will understand the reasons why your game won’t ever be released, don’t worry about that. Explaining your reasons a billion times will just remind you how awesome and awaited was your game idea, and how many disappointed people you have made. In this business, disappointing people is not a great strategy.
Don't fear the ugly copycat
One of the most common reason why people don’t talk about a game is because of the easiness of copying it. If you have an awesome game idea it’s natural to not want someone else to steal it and make money out of it. Your idea: your money.
Please don't believe such thing is even possible. If you take two game developers and give them the same game idea and the same development conditions (money, working place, team skills, machines, free coffee... etc), you can be sure that the two games won’t be the same. The core concept might be very very very close, but final games won’t be. An idea is just an idea… the way you will transform this idea into a game will surely be very personal. Take into account your team with its very own set of skills and you can be sure to have a very unique game.
Of course exceptions exists and there are two main categories: the copy for money and the Game Development entropy. One is a concept copied on purpose to try to make some cash out of it. The other is a pure chance, because we all evolve in a world where we read, see, and think about the same content, it can happen that two of us, even in distant countries have the same idea at the same time watching the same movie or reading the same book.
Yes, I know you know about Threes and 2048… but the simple fact that you actually know about these two games should show you why you should not fear about your game concept being similar. After all, if you know about these two… it means that they have enough echo to both be a success. Also note that Three and 2048 are games for smartphones. The gaming community on PC and consoles has different costs, expectations and habits, that’s why such cases are “uncommon”.
Don't see enemies everywhere
Sometimes you go to game developer events and you know you will meet publishers who might be interested in putting some coins on your game. You have great expectations for these meetings (often too great) but you wonder if these people, with too much money, won’t listen to you just to steal your idea. You’re just a tiny indie developer… they are so big and so mean why won’t they?
Some fellow (new) game developers often ask me if it’s ok to ask Ubisoft, Sony or Microsoft to sign a NDA document before talking about their game concept to their representatives at a local game developer event. Come on…
If you have ever worked in a team you should know how hard it is to grasp 100% of a concept when it’s explained using only words. If it’s so hard to explain such a thing to people you work with for years don’t worry about this suited person who doesn’t care about you and your stupid idea.
It’s actually pretty rare that gigantic publisher are interested by ideas. They want prototypes. They need proofs of concept. An idea is worth nothing… Everybody has ideas.
The perfect timing
In the end there is no perfect timing to talk about your game. You just have to feel prepared and be sure that it has great chances to be released one day. Don’t live in the fear to see someone else making the same game, because time spent being scared is time spent not making your game. The more you will wait before releasing your game the more probabilities to see a natural clone (born from a common reference, not copied) will raise. Ironic, isn’t it?
I’d suggest you to start talking about your game when you already have something to show. A video, a playable demo, fake screenshots… then, in the head of your readers you will have a game in development, not just an idea.