Yeah, I think without a shadow of a doubt we will see Wolf.
But, when, I have no idea.
To go along with what @
jahkzheng
said, I actually thought of a similar theory when Ryu and Roy were first found.
Judging by the fact that Ryu and Roy have virtually no files besides music, and absolutely none on the Wii U, I think that they were accidentally left behind, and Wolf is actually really far along. I do remember a rumor after the game released about Lucas and Wolf sound files being found in the game. This was after Mewtwo was announced. If this is true, it could simply mean Wolf was already in development before Mewtwo was even announced.
I think the whole thing about finding 5 slots in the code for more characters EVEN FURTHER supports Wolf, because why would they randomly have 2 other slots in there for no reason? I think this means 2 other characters are being worked on, my guess is Wolf and Inkling. The Ballot is not even finished with yet, why would they have planned out exactly what/how many characters already, 8-9 months before it even ends?
E3 will be a time of celebration. My guess is Wolf, Ryu, and maybe Inkling at E3, with Roy at the Fire Emblem Concert.
Hopefully.
If this happens I think I would be fine if there was no more DLC even.