Can the pendulum style takeback be combined with a straight arm and WW finish to expand the hitting zone and provide more spin variation as a "base" forehand style?
Technically, no. A straight arm configuration is really a reflection of the extension through the shot. When you use a pendulum-style takeback from a static position, you get the best extension when you use a down-to-up forward swing, finishing over the shoulder. If you swing in an across, WW-style, you'll have a bent-arm configuration. (Again, we're strictly talking static position.) Sampras used both kinds of swings, but I think he wasn't especially conscious of this.
There's ways to add more spin variation, though. Federer's rotation on his takeback was also done by Laver, and it gives you a more lasso-like motion while still retaining the basic pendulum shape.