I didn't watch that final, but I know what you're generally getting at with the two-handed shots. Bartoli is certainly an interesting player.
One advantage to hitting a drop shot in the same fashion as the topspin stroke is the inherent element of disguise. The drop shot is most effective when an opponent can't see it coming and get a jump on it. Since your backhand slice is a one-handed shot, I don't think you'd have much of that disguise if your dropper was a two-hander with that tell-tale high-to-low racquet motion that includes an open face.
If the reality of the drop shot for you is that you can't get the touch or stability that you need with a one-handed style, then you probably need to consider a two-hander if it simply clicks for you. I think that a full backhand slice has the best potential though, when it's hit one-handed. Since the wrist remains firm through the stroke, a two-handed slice puts the swingers arms more in opposition to one another.
The two-hander can bring a lot of extra power, stability, and quicker execution as a topspin stroke, but a slice depends much more on proper mechanics and timing along with the one-handed aspect that produces the right swing path.