After listening to some of the tracks from the G98 score, I wouldn't necessarily mind if David Arnold came back for this one. His main theme for that movie was actually really good, the kind of thing I could see the real Godzilla showing up to. Not saying the guy would be my first choice, but it wouldn't sit poorly with me.
As for the Ifukube debate, I feel like his music could be used in a more roundabout and/or subtle way than playing one of the classic themes over the credits or Godzilla's appearance. One thought I had would be to play the Monster Zero March or a similar theme as background music for a military training/recruitment video. That might still be too on-the-nose for some, but I'd be cool with it. Alternatively, why not use one of Ifukube's non-film pieces instead? I can, for example, imagine part of his Violin Sonata (
www.youtube.com/watch?v=Q4WTjU5hH-M ) being the BGM in a fancy restaurant or something like that.