Contextualized theme ?

While hacking into `react-with-styles` in order to integrate `react-dates` in an application that use a different style architecture ([gist](https://gist.github.com/Volune/4e21cd7e72804c3a3b22778af6bbb8cc)), I realized that both the Theme and the Interface are *singletons*.

So if I understand well, it is not possible to have two customizations (use two different themes) for the same component in different places of the application.
Am I missing something? Wouldn't it be better to rely on React's Context (or another alternative)? What are the recommendations?

I'm asking by curiosity, I don't have an actual use case.

Start by reading how Theme and Interface are implemented as singletons in react-with-styles, then review the React Context alternative raised in the issue. Determine whether separate component subtrees can use different themes and interfaces, and document the recommended approach or the design needed to support that behavior.

Written by the indexing model from the issue text.