Rasterio 1.0b2 is on the Python Package Index today: https://pypi.org/project/rasterio/1.0b2/. This release has been blocked for a couple weeks while we worked out some issues with Rasterio's boundless reads, WarpedVRT, overviews, and masks. To try it out, run pip install rasterio==1.0b2 in a new Python environment on Linux or OS X. Conda packages for Linux, OS X, and Windows will be available soon from conda-forge.
There's a breaking change that I couldn't avoid in 1.0b2: boundless reads from a WarpedVRT are forbidden. I never intended this to be a Rasterio feature and removing it is in my view as much of a bug fix as it is an API change. If you're using software and see errors that report "WarpedVRT does not permit boundless reads", you can downgrade Rasterio to 1.0b1 while that software catches up to the changes in Rasterio 1.0b2.