Developed by German C64 coder and hardware expert Frank Buß, the cartridge will feature not only full MIDI in, out, and thru support, but also a possibility to directly transfer PRG files from PC via USB. It comes with SIDWizard and Steinberg Pro 16 pre-installed. The design and firmware will be open source, so you can build this beast yourself as well, if you're feeling lucky.
Even if you're not interested, you gotta love the guy's thick Colognian accent ;)
Read up on the details on the fundraiser site and preorder the cartridge or donate a few bucks to the project!