Well, "games" are interactive. So I hardly think something could become a game by becoming less interactive.

I think when people say "Yeah, this isn't an idea for an RP, this is an idea for a [i](insert chosen media here)[/i]," what they are actually saying is that the idea is too cool/good/sensational to be made into a crummy ol' RP, and you could instead use it to make big bucks. The problem is that there's an uncomfortable truth that separates the Hollywood blockbusters, the triple A game titles, and the best selling novels from anything you're going to write on this forum:

Ideas are only worth the ambition you pour into them.

Wanna turn an idea into an RP? Pretty easy. Just put up an interest check, post weekly, and you might be blessed with an RP that lasts for years. It might even have the word count of a novel or two by the time you're done. I think my danganronpa RP had a word count long enough for 3-4 novels. 

Could I turn it into a novel series? [i]Hell no.[/i] The first hurdle is that it's fan fiction and wouldn't be legal anyway. If we ignore that, I wrote it with at least 15 other people. If I wrote 2k words a day, I [i]might[/i] be finished in a year. But we're being very generous if we assume I'm able to keep that pace or that it's the final version. chances are it will need extensive editing. I'm not just talking typos, im talking huge things like entire conversations vanishing because they add nothing to the plot, and different scenes springing up in their place. I'm talking about finding inconsistencies, the type of stuff that would bother the most critical person in your writing circle. [i]Because you know what? They have nothing on what a reader who pays for your work will expect.[/i] And after you've sunk all that time and money into editing and finally think it's perfect, you'll have to face wave after wave of rejection from publishers who just don't think it's good enough yet, or maybe you self publish and take on the nightmarish task of trying to market your book so that people will actually read it. 

And books are easy mode. Just imagine the effort it takes to make movies/games/tv shows. Have you seen the credits to those things? That's not something a small group of people can just do. 

So the short version is this: there is no idea that wouldn't work for RP. It's the level of ambition you wish to devote to it that decides if the effort is too monumental for it to be considered an RP anymore.