Since Android 4 has some nice new APIs, and since Android is Open Source, I've thought, Why not, for the time being, use the new APIs as if they are a part of the application, and when the time is right (when most users use the new version), use the official APIs instead?
For example, I think that the GridLayout, and maybe other new stuff, could be imported into projects.
My question is: Has anyone done such a thing? and if so, How well does it perform? Also, if anyone has done it, please publish a project, so that everyone could enjoy it.
I also wonder why Google doesn't provide such a mechanism in order to give more power to old versions and also to get rid of deprecated things.
google does have some support for features of newer versions. for gridlayout , it's possible to use something like on this example: http://code.google.com/p/android-playground/source/checkout
for actionbar and fragments , there is the support library and there is the actionbarsherlock which is based on it (not created by google, but very good and even better ).
There are a few backports of new features to older devices available. The most prominent one are probably the Fragments from Honeycomb. Also this "slide to change tab" (ViwewPager) feature of e.g. Google+ app is available in such a compatibility library.