Over the past couple years there has been some coordinated correspondence forwarded to NEF from members of this site offering suggestions for new calibers. Several of the calibers suggested have been produced, though not always with good results. It would seem that they do hear our suggestions. So, I would say to contact them with any caliber suggestions you may have.
It seems logical, at least to me, that with the popularity of the .357 Mag over the last couple of limited runs, that they would produce that caliber as a complete offering.
Also, at this early stage, it would appear that they may have hit a home run with the .444 and .45 Colt.