I feel Vulgar Reverie did this really well an update or two ago, when you get the first NTS BJ scene. The trust (and intentions) between MC and FMC is established very, very thoroughly, but it still plays around with MC being anxious about it actually happening for real, and it is (from what I can remember) still left as kind of a "one day, but not right now, so just tease him for now" type step for them to take in their relationship, but the FMC goes ahead with it of her own volition, and then texts MC about it, so she doesn't hide it from him for very long at all, but she still...takes the initiative and jumps into it. The whole thing was just super well done, in my opinion. On the edge enough to be exciting for NTR enjoyers, but still within the lines of appealing to those looking for NTS as well.
With that said, I like both NTR and NTS and don't mind whichever way it goes, but I generally agree with your post. I hope the developer doesn't get too discouraged by the whiners and isn't afraid of putting people out of the comfort zone a little.