I really don't think you will see traffic added to the Stratus, but I can't speak for them. That said, ADS-B Traffic is really not something to hang your hat on. Only an ADS-B Transciever or In/Out device will give you a more respectable representation of Traffic. The big issue is the an ADS-B receiver with traffic capabilities only shows ADS-B out equipted aircraft. The TIS-B broadcast does not send out a blanket traffic area. Therefore you really need the ADS-B out functionality to report your GPS position so that the TIS-B broadcast can be sent for your coverage area.
Many of the ADS-B receivers are totally omitting Traffic due to the liablility involved and the lack of consistant traffic. The 2020 Mandate is for and In/Out device. This is what will be needed for the best accuracy. That said, there is not replacement for keeping your aircraft spotting skills up in VFR conditions. Non-electrics and Aircraft flying on a waiver will not be shown on any TCAS or traffic system. ADS-B Receivers are really fosuced on WX with no reoccuring fees. Some ADS-B companies chose to include the limited and partial traffic. It is very risky.