yes, FreeMASTER-over-LIN is still a bit experimental feature as it needs pretty specific support on the target side (multi-frame transport layer, diag-class II or III). There were just few users interested in this solution so far, so the PC support has not evolved more than to a single NI USB-to-LIC device support.
The situation with FreeMASTER-over-CAN is different. There are many users and wide support for different CAN hardware including Vector, HMS Ixxat, Kvaser and others.
Can you tell more about your target application? Do you use NXP LIN communication stack? What is your target platform?