I'm curious if Sony is going to offer the firmware upgrade for the existing models like A7II and older.
Yes, they introduced it with the a7SII and will update a selection of cameras:
Additionally, they have announced plans to add user selectable compressed or uncompressed 14-Bit RAW still image capture via firmware update to additional cameras beginning with the recently introduced α7R II full-frame mirrorless model.So after the a7RII probably the a7II and hopefully my a7S is next in line.
At 12MP is don't care about the increased file size btw, bring it on