If by that you mean a fully functional handheld GPS with an integrated PLB (as opposed to a PLB with an integrated GPS receiver as is already available) , don't hold your breath. People want their GPS, which they use all the time, to be small and light as possible. While PLBs will be getting smaller, the power requirements for the PLB, which must be totally discrete and separate, will always dictate a battery that's bigger than many entire GPSes. Just not practical and likely never will be.