Should a feasibility plan be created before the game?
If you are serious about selling your pride and joy, then yes, and no. It depends but in all cases, a feasibility plan will be needed if you plan to produce the product.
Let me explain:
Let's say you have plans to create a deck building game. You have a great idea and you're really excited about it. Okay, now what?
People invent so many things and then they never get it to market. They spend hundreds of thousands on prototyping and development and learn that they should never have started the project in the first place.