Recently I was watching the Ultimate Spider-man episode about Doctor Strange (I know this show doesn't really match the comics). A thought crossed my mind when Iron-Fist mentions training with Doctor Strange, the thought was that Dr. Strange could appear in the Iron Fist Netflix series. This could happen in many ways.
1) [Doctor Strange](movie:559685) appears in flashbacks to Iron Fists training in the mystical arts.
2) Doctor Strange is teased throughout all the series to finally be completely shown at the end of the Defenders series (assuming the Doctor Strange movie hasn't come out yet) leading into a Doctor Strange movie.
3) Doctor Strange is one of Iron Fists most trusted allies and advisors when he needs help and he appears frequently throughout the show.
This could also be a reason that marvel is looking at Joaquin Phoenix as Dr.Strange with him not really having huge Hollywood star appeal, and may be fine with also being in a TV show on the level of Netflix.