Well, I mean, I will wait and see. I have shelled out big bucks before for a non-dining plan restaurant but I only like to do that if it is truly an out of this world experience like Victoria and Albert's - I've done them several times and did feel it was worth every penny. Perhaps, this place is on that rarefied level to be worth dropping a few hundred bucks at though I probably don't want to spend that at this point in my Disney vacation journey anymore.
Also, as someone who has eaten at Monsieur Paul and Bistro de Paris (it's former name) many times, that is a place where I have NEVER seen anyone who has ignored the dress code, as I have often seen at the other signatures do. I mean, you would really feel out of place there, too, if you showed up in tank top and torn clothing (just an example), in that all the wait-staff are in tuxedo-like attire and the tables are covered with like white linen (or something) table cloth. The ambiance there just feels ritzier than at California Grill - I mean, they even have it set up so you have to check in away from where everyone else is eating, so I feel like they can check you out downstairs and perhaps won't let you upstairs (where the tables are) if you don't measure up LOL.
That being said, I don't dress any different for Monsieur Paul than I do for California Grill or the other signatures. I always wear one of my nice khaki or similar style dress shorts and a polo-style collared shirt and my clean new balance sneakers. That's always been good enough there, just as it is for all the signatures. And would be similarly fine, I am sure, for this new Japan signature.