Fall - Winter Timeframe
According to a friend who works on weather-in-the-cockpit policy / research at what used to be the FAA's Small Airplane Directorate (changed to something else in a big re-org last year) the new ADS-B weather product documents from RTCA* would be published in June, with final approval of the new products expected in the Sept. - Dec. timeframe.
If I understood him correctly, implementation of the products - actually uplinking the lightning, cloud-top, and icing reports - would take some time. The final docs released in the fall / winter would contain the information that EFB and MFD developers need to add support for the new products. I don't know exactly when the towers will start including the data in the FIS-B uplink.
* RTCA is an international industry standards association for avionics.