Good news everyone! Today is a day when the great devteam of HLAE released the script to import .BVH. Script was developed by R.I.Pieces and is capable of importing the keyframes on an existing camera inside SFM clip. Unfortunately right now BVH file is not containing FOV info and thus it has to be set manually. Readme.txt that goes along with the script contains instructions regarding both: the basic how2import and a link to the forum topic where FOV calculation formula is explained.
Export script right now is in development. Stay tuned!
Update: Export script is now live. Hurray!