I'm working on adding touch-to-drag and pinch-to-zoom support for matplotlib. It is in general working but there are a few things to add before I submit a pull request. Wanted to get the conversation started though on a few points, and ask for any general input from the community.

Specific points:

1. Is this a good idea (I can't think of a reason it wouldn't be, but advise)
2. Should it be a toggle-able feature, for example in the rcParams? (I can't really think of a reason it should be, but maybe there is a use case in which people want touches to behave as mouse input)
3. Pinch to zoom in my implementation keeps the same points on the plot under your finger. So x and y axes rescale independently and aspect ratio changes as you move the two touches. Sounds reasonable? (this is intuitive to me)
4. Key input should hold x, y, aspect ratio (ctrl) as it does for current interactive mode. But maybe there should be some other situations in which we hold x,y: for example if the two touches are at approximately the same y-value, small changes in their y-location will lead to huge scale changes for the y-axis. So maybe if the touches are sufficiently close on an axis, that axis should be locked?

Open to any other ideas!