As mentioned in the spoilers for Smackdown. Big Show had fans start a "yes!" chant for a video that would be sent to Daniel Bryan. Show told the fans that Bryan likely needed another surgery.
According to his segment was not taped to air on SmackDown so it appears the video was done just to cheer Bryan up. It's always possible they air it at a later date.
Regarding Bryan's status, a WWE source says there is no timetable for his return and no guarantee that he will be able to return.
Officially, WWE has been very quiet on the Bryan situation publicly but wrestlers have been talking about Bryan needing major elbow surgery. There was talk of Bryan needing Tommy John surgery, which has a long recovery time, but it's not known if that is the surgery that Big Show was referring to.
A few people were asking what audio was playing when Bray Wyatt interfered at Hell In A Cell, According to Wrestling Observer Newsletter, The words that played when Bray Wyatt made the surprise return was actually an old Wyatt interview played backwards.
Regarding the hologram that appeared, apparently people in the company saw this at a concert and thought it would be cool.