Well, at the moment it does not look like a third expansion is in the plans, and from what I have seen so far, I guess Blood and Wine will probably not include significant content involving characters from the main game (I mean not just a few lines of dialogue like in HoS or other minor addition for continuity). Regarding the enhanced edition, it is not known yet for sure if one is going to be made, let alone with major new content, but it is discussed in this thread and this one. Others possibly relevant to the topic can be found here and here.
