I released Rasterio 1.0.25 yesterday. It has a few important bug fixes, but the core of the work was writing and testing shims to make the package compatible with GDAL version 3.0 and PROJ version 6. Norman Barker did much of that work and I only had to make sure that we were using the right coordinate axis order strategy everywhere and figure out which of the output changes were new Rasterio bugs and which were actually improvements delivered by PROJ 6.
Please note that the binary wheels for 1.0.25 on PyPI contain GDAL 2.4.2, not 3.0, and that no new features of GDAL 3 and PROJ 6 are intentionally exposed in Rasterio's API. My wheel builds are already running up against time limits on Travis CI, and GDAL 3 and PROJ 6 take even longer to compile. My system is going to need some more hacks before Rasterio wheels with the latest GDAL and PROJ are possible. You might be able to get a combination of Rasterio 1.0.25, GDAL 3, and PROJ 6 from conda-forge. I look forward to hearing how that works for users.
I hope you'll appreciate that I've managed to shrink the size of the GDAL shared libraries in the manylinux wheels by 50%. I wish I knew why they are so much bigger than the OS X libraries. I suspect it's due to the ancient toolchain and glibc used by manylinux1.