Right - you found it out yourself. We're currently supporting Mifare Classic (1k).
We are very aware (as we've indicated before
viewtopic.php?f=4&t=439 ) that the Mifare CRYPTO1 algorithm is broken. However, given the spread of Mifare Classic it has been a pure business decision to go for the Classic 1k track. For most access control application, it still works - although with a lower security than claimed (by NXP/Philips). Compared with the commonly used "proximity cards" which just emits a static ID however, Mifare is a different leauge.
We have got a few requests for other 13.56 MHz standards and we will eventually switch over to the Mifare Plus later on. If you have some project in mind, we may make some special DESFire or Plus Yubikeys available. Plus chips are still a bit difficult to get hold of "in reasonable volumes".
Please let us know your thoughts. I am happy to take off-line requests at jakob at yubico dot com if you don't want to discuss it here.
With the best regards,
JakobE
Hardware- and firmware guy @ Yubico