No, Nintendo has to prove that they will give all dlc fighters a highlight.IMHO if Reimu was happening, she'd have been revealed last month, since there's zero benefit in having her be at TGA unless for whatever reason a Touhou game will be there. Which is doubtful, as Touhou is a very Japan-oriented series, as in they don't make decisions based on the demographic outside Japan.
I'm certain that whoever #5 is must be also promoting a game world premiering at TGA, and at this rate is honestly unlikely to even be a third party at all.