The highest grossing Godzilla film in the last 25 years was Godzilla vs Mothra, and it only made $20 million. The most recent film Godzilla Final Wars only made $12 million. The genre hasn't been a major box office draw in decades. King Kong vs Godzilla is still the genre's high water mark and that was 50 years ago.
Do you have numbers for Godzilla (1998) in Japan? I can't find them, but based off its respectable overseas gross for the era, I would imagine it did better than $20M in Japan. There has been nothing but low budget domestic monster movies between that and Pacific Rim.
Plus, Evangelion 3.0 did $60M in Japan last year. There's a market for mechs if not monsters. I don't think big grosses are a lock by any means, but I think the film will perform pretty well in the territory for a Hollywood film.