For anyone still watching this thread and hoping for an all-in-one solution, rather than having to use two separate pieces of software as lordelan suggests, I am looking into this now.
I've finally managed to compile the most recent version of WiiU-Shell from
@GaryOderNichts' fork (thank you so much Gary, couldn't have done this without you!) and it works reasonably-well for anyone interested in just the SD card. You can grab the RPX from
https://github.com/kenny1983/WiiU-Shell/releases/tag/v1.06.
I still have a few minor bugs on my console, which I'll try ironing out before attempting to add USB, FTP and cloud support (in that order).
Oh and the ability to edit text files and extract archives would be nice too IMO, so I'll try to look into that as well :-) If I've missed anything, just let me know! Peace