MapR-FS provides transparent compression at the filesystem level - it's a very good idea.
It could be done on a directory basis (like MapR) with specific subdirectory and file / file extension exclusions, such as a .ignore_compress file in the directory.
Keeping files in plain text format makes it easier to use different tools on them without worrying about codec or container format support etc, but currently one can pay an 8x storage penalty for keeping uncompressed text.
This would solve some real problems for us right now if we had it. It's also annoying that many tools are always showing reading textfiles but this is so costly on storage without this transparent compression. We actually are stuck with a large historical archive of compressed files we can't work with (no zip inputformat) and can't leave them uncompressed either because of the storage waste which would exceed our cluster capacity. Having to reprocess them all to convert to different compression and then hope all future tools can handle that format is far less ideal than just having transparent compression.
The increasing proliferation of tools and products on Hadoop exacerbates this issue as we can never be sure that the next tool will support format X. Everything supports text. Please add transparent compression to make working with text better.