It's called royalties payment and is nothing new. Whether you prefer this method or a fixed amount is up to you (as the developer of the game), both parties usually agree beforehand.
This is the key, right here. And from a proven, reliable, and
knowledgeable, experienced source, no less! I respect everybody else's opinions above, however, it is really up to the game developer as to their pay structure. Now, will they have challenges in finding quality workers who will work for free up front, and for a payout
if the game makes money? Likely. Will they encounter personalities that say, "I'm worth more than a promise! Pay me, or I won't work!" Certainly! The whole film industry is filled with examples of these types of arrangements.
Let me give you an example of how this could play out in the game development world:
The New Game Developer comes on the scene, and learns everything he can about the RPGMaker program. He has (what he believes to be) a great idea for a game that's going to be fun and unique, and isn't going to be just another entry into a saturated genre. It offers gameplay that will be interesting, a story that will be engaging, and some replayability. He/She chooses to develop a 'prequel' to his/her game, and to develop it all his/herself. Months later, he/she releases a demo to a small group of playtesters, fixes the bugs, tweaks the elements they agreed were lacking, and releases it to the public. He/She does some basic marketing, spends a bit of money, and overall, receives positive (fair-to-good) reviews. Now, the New Game Developer, with some experience and knowledge under his/her belt, decides to create "the" commercial game. He/She polls the local talent, and armed with his/her experience and positive 'word of mouth', asks for volunteers to provide some graphic, music and scripting work, with the agreement that if/when the game is released, those involved will receive royalties based upon their involvement as well as the game's success. Everything is written into contracts or agreements, and everything is understood and agreed to before any work is done.
With the above model, there is still the important question of "
will the game sell?" Obviously, this is the pink elephant in the room, however, here are a LOT of positives in regards to the way the New Game Developer went about asking for help. He/She gained experience by working on their own, made a 'free' game, to showcase his/her talents, and made sure that everything was in writing, understood and agreed to. These three items make it a lot more convincing to those who will, in the future, agree to work with/for such a developer.
Of course, this is but one example of some positives within the whole 'development cycle'. There are a far greater number of examples than I have quoted here, in my limited experience, and a greater number of examples of 'bad ideas' in the course of attempting to garner new talent to your project.
In my own project, I'm presently on the 'learning as much as I can' part of my example, and am working towards releasing a free demo of my own game series. I'm not going to say that future releases will be commercial, because I'm not at that part quite yet. Personally, I need to see what the first release receives by way of criticism and praise, and then I will determine whether or not the next release will be for profit, or a continuation of my learning process. For that, only time will tell.
GB