Yeah I agree, new ideas need to push boundaries, but I would still fail to see how a programmer is not capable of pushing boundaries also, especially if he is already taught not to take his latent knowledge into account.
I'm not suggesting that a programmer is incapable of pushing boundaries, I was trying to say that whether they can push boundaries or not is unrelated to whether they can program or not. As a designer, they can either "think outside the box" or they can't. Whether they can program or not is entirely seperate.
On the question of pushing boundaries with say, head capture technology; are you making the assumption that it was a bright spark with little programming knowledge who came up with the idea? Or was it a highly technical person who came up with it? I know who I would put my bet on.
I was using motion capture to illustrate the point since it seemed quite universal in my mind. Most people would understand that motion capture wasn't available at all years ago, and now it's getting to be more commonplace. Someone had to come up with the idea, rather than thinking about the fact that keyboard/mouse was what worked.
It was simply to illustrate the point that to create you shouldn't be limited by foreknowledge.
This still does not solve the issue of where a Game Designer fits in with a team. Like I said before, I fail to see how a pure Game Designer is capable of coming up with new ideas that a programmer/designer is not capable of. It seems like a straw man argument to say that a Game Designer can push boundaries and a programmer/designer cannot; it is an assumption based on opinion.
Some teams don't need a dedicated game designer, I would hazard a guess and say almost all small indie teams do not have one. A programmer designer is perfectly capable of coming up with a great game. This isn't because he's a programmer, it would be because he's a great designer, he just happens to also know how to program.
If you have a good programmer, and a good programmer/designer, you can make a good game.
If you have a good programmer, and a great designer, you can make a great game.
Of course, the great designer needs to actually be 'Great' in order for the distinction to work. Whether he can provide value in his role purely as a designer. This depends a lot on the team; what roles you have, what roles you need to fill, and so forth.
A good designer should add value to the team. You have to consider whether this value is worth it, the same as with any prospective member of the team.
If you have a team of 3 programmers making your game, they're working easily to deadlines, meeting quality requirements, and a 4th programmer applies. You don't automatically hire him because he's a programmer and he can code. You have to question if his coding is going to be worth having a 4th programmer around.
If this 4th programmer can prove that he can halve your development time, while decreasing workload, and exceeding the quality you're looking for, then it makes it much more appealing because he's proven his worth.
Proving your worth as a designer is an abstract thing, and it's what I'm really interested in. How do you prove that you're a great designer? Whether a team needs a designer is dependant on the team. But you need to showcase your ability so that they can see how good you are, the same as with any role.