It would have to be gas tight, and resist a pressure differential. (HSF heatpipes contain water in a partial vacuum) It must also not leak at all over the cour

It would have to be gas tight, and resist a pressure differential. (HSF heatpipes contain water in a partial vacuum) It must also not leak at all over the course of several years at elevated temperature, while spinning at several thousand RPM, or else the heat pipe will stop working. It also must be cheap enough to compete commercially with a solid piece of metal. The design constraints are... loosely possible. But it sure as hell won't be cheap.