Maybe you could think of a better way to do away with the antiquated thumb stick.

I'd like to see touch pads continued; I like how the iPhone is used without a stylus, for example. There wouldn't be a need for d-pads anymore, which seem clunkier as time goes by.

Trackballs I'm not so sure of; the continuous movement that a stick can be provided simply by holding it down can only be replicated with a trackball by repeated twisting. It offers more precision on small movements, but it's convenient for longer ones.  

I dunno. Touch pads can be nice, but there are two major inconveniences that I can think of off the top of my head:

• Ever used a touchscreen-only remote control? They look slick and all, but you need to look at the screen to see which button you are pressing. With hard buttons (traditional remotes) you can feel the unique shapes and sizes of buttons which means you don't have to keep an eye on the remote in order to switch channels (which implies you take your eyes off the TV). Now put that into a gaming context and the problem is rather apparent.
• Just imagine trying to pull off a "shoryuken" with a touchscreen!

True, but then that kind of negates the inherent flexibility of a touchscreen, doesn't it?

With raised bumps, you essentially are assigning button areas to the touchscreen when the beauty of having a touchscreen is its ability to adapt to whatever use the application needs it for. If the surface of the touchscreen needs to be raised in order provide tactile feedback, then what's wrong with having buttons in the first place, since it accomplishes exactly the same?

Also, while any control mechanism can be learned and mastered, it doesn't necessarily mean that it's better.

I'm not sure either of this is really a problem. I've yet to see a game controller that has as many inputs as your average TV control, so it's not realy a valid comparison. The standard diamond-shaped pad can easily be recreated, as its four inputs in a rather large area, while a number pad has nine over a relatively smaller one. No one really looks down at the similarly-shaped face buttons on an Xbox or PS controller, because with a bit of practice your thumb knows where to go. 

As for the second - just touch your thumb to the bottom of the pad and sweep it counter-clockwise for a quarter, and then press whatever corresponds to "Punch." To my mind this is quite a bit smoother than even the Xbox d-pad, which makes an effort to facilitate continuous motions.

Good point.  Maybe a touch screen isn't the best solution.  Perhaps face buttons aren't really an issue at all. 

But what do you think about a track ball in place of the primary thumb stick?

I don't know if that would work. In order for you to feel those raised bumps you have to touch them, which will activate that button.

Here's another problem, how would you hang on to the controller? You can't have your thumbs resting on top of the screen since it would activate buttons. I imagine having your thumbs floating above the controller would be tiresome.

Touch screens also doesn't allow more than one simultaneous touch. How can you pull off Zangief's spinning lariat?

I feel it would be a major issue as up to now I can't think of a DS title that utilizes the touchscreen that doesn't require you to fix your eyes on the screen to know what you are doing.

Well, with Mario Kart DS you just have to tap anywhere on the screen to switch between map modes, but then again, the touchscreen in this case serves only as a toggle.

Regarding the input issue: Let's compare a gamepad with a phone. They both have about the same number of buttons. I don't think you can dial a number on a touchscreen without looking at it. You can, however, do so with a phone with hard buttons.

I don't know how the iPhone handles this, but if they have come up with a way for you to dial a number without having to look at the touchscreen then I agree we may have a winner. Otherwise, I think touchscreen either needs to mature more, or perhaps there are other alternatives out there that are being researched. 

If I'm not mistaken, the iPhone supports multiple touches. This is more an implementation issue than anything else, seeing how Apple bought out those two researchers that devised it in the first place to get their hands on this technology.