API: Return BoolArray for string ops when backed by StringArray
ref https://github.com/pandas-dev/pandas/issues/29556
Do we want to optimize the BooleanArray first before returning it from methods like this? I think could have non-trivial memory impacts doing this right now Recall this is just for StringDtype, not object-dtype backed Series. So there's no harm to the current users.

And improving performance later is much easier than breaking API. Planning to merge this in a few hours. > I'm going to hold off on this. I'm planning to restructure the docs for integer / boolean / NA once all these PRs are in.

What's your current plan? 
In one of the PRs we discussed a little about this (gather them all on a single page vs additional nesting), but don't know where any more.