A first beta version of PyarrFS has been released, or well, at least made available via git. To save myself some work, here's merely a copy of the overview from the PyarrFS page:
PyarrFS is a FUSE based file system to access the content of RAR archives as if they were just normal files and directories. PyarrFS owes technically to FUSE and rarfile, while the idea originates out of YarrFS - a similar file system I came up with a few years ago. It works with both compressed and uncompressed rar files, though due to a bunch of stupid reasons we need not go into detail on here the support for compressed files is much worse than that for uncompressed ones.
Go to the PyarrFS page, to download. Comments, suggestions and patches are of course very much welcome!