Sadly there's not much incentive for Moonbox to actually pull the trigger on that for the foreseeable future.
Depends, it seems he does want to do other game(s) in future and also though it can be scary to say goodbye to a game that makes you good money and have fun making, if want to go the steam route it seems having more as 1 game finished is even better as having one very long game. So it may well be in the devs interest to pull that trigger sooner as later. Especially if still holds true what dev said in past that sex Nana would be halfway point of game or story.
Now I think either of Nana or Jamilla would make a great x-mas present as game stands at the moment, both have burned and ramped up to a place where it can make sense to happen now, but also are at a place where unless Moonbox already has a specific trigger in mind to make them make the last step it could be easy to get into a holding pattern with them. Edit to clear up this is my personal feeling, It is the devs choice though and his story, so he decides if and when and how to trigger those final steps.
MC will not force either of them and has no real reason to push much as both Nana and Jamilla seem happy enough and it is not like he is starved for attention (hell just the Redheads in game should already be enough for every even overly horny MC
) and emotionally he already gets all from those two he needs as well. To be honest I am almost as curious to what Moonbox will do as trigger as to the scenes themselves and if will be more emotional, humorous or in the end WTF.
I would not be surprised though if in the end pervy, cute innocent curious Shizuka would provide the trigger with Nana and that we need her scene first, but dev can have completely different plans.
Amy even if may be last to fall I am in the end way less worried about, both Nana and that blonde lady without any self control are quite aware Amy is not really happy the way she has limited herself due to what happened in past and will push MC if he does not himself.
