We challenged ourselves to create a visual language for our users that synthesizes the CLASSIC PRINCIPLES OF GOOD DESIGN with the innovation and possibility of technology and science. This is material design.
Note the capitalized words: CLASSIC PRINCIPLES OF GOOD DESIGN.
We won't find whether or not we should maintain list state in Material guides for tabs
because this isn't a visual guideline. The question is more about implementation detail.
But Material Design puts an emphasis on CLASSIC PRINCIPLES OF GOOD DESIGN.
When it comes natural, then it's basically a good design.
For example, when we turned off our TV while we're watching channel 7, just to take a short break. We went to do some groceries, then came back.
Then when we turned the TV again, do we naturally expect the TV to start from channel 0 or channel 7?
Another example. When Google Chrome quit unexpectedly. Then we open it once again. Unless we have set a preference, reopening the tabs is the natural thing to do. Well at least, Chrome asks us about this. And most of us, click 'yes' when it pops up.
We love to come back where we left off. This is the point.
Now, whether Google has a guideline about this. Then answer is, "Yes they do." But since this is an implementation detail, we won't find it in Material Design Guideline (Sorry for repeating myself).
But instead, we can find it here:
onSaveInstanceState() and a specific article above, they're telling us how to implement this across our app to create natural user experience. Something that is based on CLASSIC PRINCIPLES OF GOOD DESIGN, which what Material Design is about.