...so let's just back up a few. First of all, I don't see anything wrong with the Clijsters photo that you pointed to. It may not be WW, but what she's doing is good stuff, IMHO. Related to that...why did you decide that WW is the only way to go? I'm sure I'll get some argument on this, but there isn't a single "modern forehand", there's really three fairly distinct variations, each of which has its pluses and minuses:
- The "reverse forehand", which is what Nadal hits. The racket face makes a circle, but stays on the hitting side of the body. Advantage is that you get tons of topspin, disadvantages are that the contact zone with the ball is very small (lots of shanks are possible), there's so much top that sometimes the ball falls short, and, to me, it's biomechanically the most difficult way to hit the forehand.
- The WW forehand, where you hit through the ball and then the hitting face stays open and makes and arc in front of the body, like a windshield wiper. Not a bad approach, because it imparts a fair amount of top, but still has a fairly long contact point with the ball, so you can hit with power, depth, and topspin. Only disadvantage is that it's maybe not the most natural finish to the shot biomechanically...you've started the stroke by going out toward the opposite court, now you have to change the swing path into a WW finish.
- The Federer forehand, where you continue the foreward path of the racket head, it goes all the way out to the end of the travel (max extension of your arm), then the racket head naturally swings through and finishes on the opposite side of the body. You can hit with power, spin, placement, and variety, and I think it's the most biomechanically sound stroke.
Nothing wrong with hitting a WW forehand, and there's also nothing wrong with hitting some WWs and some Federer forehands...and even hitting a "squash shot" forehand when you're stuck and the ball gets behind you. But that kind of variety means you have to be comfortable changing your swing path, as needed...and probably your grip, too.
Any shot can be done with just about any grip, but there are grips for each variation that make the swing path and biomechanics easier. For a squash shot forehand? Definitely a Conti grip. For a Nadal forehand? Definitely a FW grip. For a Federer forehand? Definitely a SW grip. For a WW forehand? Definitely either a SW or FW grip. If you want to try to hit a WW forehand with an Eastern grip, be my guest, but it ain't gonna be easy...