About NFC readers, for now only SCL3711 was tested, and sadly not reported working. Though it’s compatible with libnfc on Linux, so it might be possible for a developper to add support for it.
If you have any other NFC reader, please test it and contribute your results here.
For your key : "The YubiKey NEO has both contact (USB) and contactless (NFC, MIFARE)"
Did you try it straight over USB ?
Mifare is also definitely an option, as a contacless reader is reported working on the above wiki.
After I received my new FP2 backplates with space for IC-breakouts I decided to give NFC a fair chance. My testing bases on the classic mifare RC522 breakout with I2C interface and FTDI’s FT201 usb converter. The challange and hard piece of work will be the software not the hardware. For the hw costs I guess the case backplate holds most of it. So I compared with typical offered usb readers around 50EUs . E.g. for ACR 122U NFC Reader an android app exists I admit it also works for FP2. My hw cost: 15EU . I wondered why FP’s decision on design studies went without it . Maybe the kernel inferface of FPOS even support more than I still know by now. However the space issue of modul integration maybe was too critical . Usually the cost I would say was not, but maybe they even tried to get below 500Eu.
Instead of kind of own driver in usb userspace FP-Open OS offer a chance to integrate OpenNFC into FP2’s android http://open-nfc.org/wp/editions/android/ . So, if you want to have now NFC turnkey ready an external usb reader would be your choice. Me as a developer I have no choice than for android integration. Because it hopefully enables most NFC apps. But I am not sure if it finds the official way into any kind of FP-OS(OS) that would be great honour to me , of course.