Sorry all for the delay regarding this one. As the COM library was designed without the Yubikey2 features in mind, we had to do some kludgy extensions to it to avoid to break the interface. Since then, we've said "Let's decide what the IYubikey2 interface shall look like" and we'll then make the 64-bit release then.
Quite a few of our customers have asked for a native C++ class or a library that can be compiled into the code, rather than having to go through COM.
We have just completed this stand-alone C++ library that we're just about to release as open source. The plan is to make the new IYubikey2 COM component almost like a wrapper of this C++ library.
We'll post an update with in a week - promise
Hardware- and firmware guy @ Yubico