The FIM *Application Kit* is nothing but an add-on kit providing a carrier board with external circuitry/components showing how to implement certain interfaces using the FIMs on the NS9210/NS9215. It's essentially a reference design. You may be fine looking a the schematics only, but you also will be able to buy one of the boards the schematics document, if that is something you would want for development.
The FIMs themselves of course are on-chip, and to support a particular interface a) FIM firmware, b) host OS API integration, and c) some external hardware (typically passive components only) are required.
1-bit and 4-bit SDIO through the FIM is supported in Linux and NET+OS today, from a software perspective.
USB device low-speed is not yet supported in Linux and NET+OS, from a software perspective.
However, the FIM application kit schematics document the USB device implementation already (the hardware part), and you could integrate that into your design today. When the software support is there, you will be able to utilize it.
Hope that helps.