First I'll start by saying, I think anything can be used if it's tasteful.
If you look at many styles today, 3d (shadows, embossing, etc..) tend to be poor in design. For example a person putting together a UI might use drop shadow because you can't clearly read the label, and that's bad.
Going back to designers like Saul Bass, what make design good is how easily distinguishable it is the user. When you look at the classic Ma' Bell logo, it's incredibly clean. The I <3 NY, by Milton Glaser is so simple and incredibly genius! Think about how that's been adapted to todays texting..
Icons for example are probably in many respects similar to animation. If you make a silhouette out of a character action (just black and white), it has to make sense to the view what their doing. You'll usually find that their poses have arms outside the body area and things are asymmetric. That's why places like Pixar spend time posing character for the camera a certain way. Icons and design are no different..
Personally I've always cycled between two extremes. simplicity vs complexity (heavy 3d / graphics styles). I'm not saying it's right, but I feel that when you have something simple like w(p)8 and its UI being very clean, you have to beef up the appeal with more animation / transitions while complexity (3d) you can do less because you're already overwhelming the user visual sense.I think Microsoft did a great job at incorporating transitions with minimal wait time, while playing with really good type design.
As for overall limitations, I feel there will be a need between simple and advanced / power user interfaces. For example, there are people that want certain features to just be a button. This isn't bad, and I'm sure certain things make perfect sense, but for me there are certain designs where I'd like to have power features available that allow me more flexibility than just having that simple button. (I'm a developer, so that might have something to do with it too

)
Anyway, good discussion!
Cheers,
Kelly