Again, Meta Knight may have been overpowered in Brawl, but he is an important and popular Nintendo character. He's worth the time and effort of nerfing. Also, referring to Brawl's priority list, he was the most prioritized newcomer next to Wario. Cutting him is unlikely since he is likely a high priority character again. Also important to mention...
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An image Sakurai drew during very early development of Smash 4.
I would think all of the characters included were being worked on at the time, or at the very least planned to be in the game. A character like Meta Knight has no way of being cut from the get go, and being high priority I doubt time constraints would hurt him at all. Factor Halberd's return into that and you have a character with virtually no chance of being cut.