I have been doing some research for an article about MEOSAR and how it will evolve PLB's. The MEO SAR Satellites will offer many advantages over the current LEOSAR and GEOSAR systems, perhaps the most interesting feature will be the ability to have a ground to beacon return link.
You trigger your MEOSAR PLB and will be able to receive return messaging from the Rescue Centre.
NOAA have a helpful diagram on their site to help explain.
Manufacturers are working on next generation PLB's, but they are a little way off at the moment, so if your in the market for a PLB, dont let that prevent you from buying a PLB now.