The rumors I heard are some models (Mackbooks I think, not necessarily MB Pros) will drop the FW400 and just have a FW800 port.
Also mentioned was support for something called "DisplayPort"...not sure what that is, exactly.
A DisplayPort in the MacBook, that oddly dimensioned port, is a distinct possibility. Here's verification of that rumor:
https://forums.macrumors.com/posts/6394030/