Games have to start somewhere, it goes without saying. Before Metal Gear was Metal Gear, it was an entirely different game housed firmly within Hideo Kojima's mind, probably packed full with crazy circumcision killers, men with firm buttocks and at least one character that couldn't hold their bladder.
It's interesting, but hardly worth thinking about. If a developer had an infinite amount of money and time, as well as a group of happy and completely open IP holders, they could make every game they've ever thought sounded like it could be good and not worry about little things like copyright infringement or losing cash. They can't though and most ideas are just that, ideas that are unlikely to ever happen.
However, that doesn't stop us getting excited for things that have long been shelved. Take for instance the idea that, before Star Wars: The Old Republic began development, Bioware bigwigs Greg Zeschuk and Ray Muzyka had several other ideas for their multimillion dollar project.
It doesn't seem like they minded too much stepping on other people's toes, they had been looking into creating another MMO based upon the Lord of the RIngs IP. This might have dropped through when EA realized they may lose rights to the series, as they did back in 2008, but what a new MMO would have done to the hugely popular Lord of the Rings Online is anybody's guess – it probably would have gone the same way as Galaxies.
Other ideas began to form around "A Game of Thrones" and, later, Spiderman and other Marvel properties. For whatever reason those ideas were abandoned and George Lucas was approached and the rest, as they say, is history (although it might be digitally enhanced in the future).