I saw his theory yesterday, and while its very well researched and well put together, nah i just don't believe it.
So much of this theory relies solely on Japanese Number Patterns and stuff only revealed in past chapters.
Plus, it would be pretty underwhelming that the One Piece would be in a location the crew already visited pre time skip.
All indications points that the One Piece is in the New World, not in the Grand Line.
In addition, although we don't know what the One Piece even is yet, it was hinted at as early as chapter 1 that the location of One Piece is in an undiscovered place, unknown to anyone except the Roger Pirates. Roger even said that you would have to search the whole world to find it.
I still think that Raftel, or Laugh Tale, being the Final Island makes sense, as the Roger Pirates were the only crew to sail the whole world completely.
I've read a much better theory on this forum that explains the ending of One Piece (the story, not the location) much better, using the same way Ohara used in his theory, drawing connections and information from past chapters.
*Edit I found it, here it is:
Questions & Mysteries - I have just figured out One Piece. | Worstgen