Not very easy if they want to maintain compatibility with existing clients (especially considering they haven't updated their linux client for years now).
Backwards compatibility with linux clients probably isn't the top priority of Skype now that they're being rolled into MS, but I suspect embedded deployments on handheld devices might still keep them from deprecating.
Actually Skype runs large clouds of linux clients (or a version of the Linux client) as part of gateways hosted with some mobile operators. They care a great deal about keeping linux compatibility.