I believe DoujinOtome has said that he doesn't know how he could make another sequel that wouldn't seem repetitive. He has probably explored as much of that setting as he could.
The one thing that I was hoping for with a potential "Spring Memories" would be for Boku to be able to unlock scenes down the storyline where there's full on interaction between Miyuki, Rio, and Yui.
For me, it's just not reached peak until mom and/or daughter/sister leans in "unexpectedly" to administer or receive oral pleasure from one of the other ladies particpating while MC pounds away.
It's amazing to me what was accomplished in RPGM with these two games when so many other products using the same engine seem so much more rudimentary. It could be though that the hiatus will allow the creative juices to replenish. He obviously knows that the games were pretty successful. For a niche product, the numbers just on Steam I thought were pretty impressive.
Maybe it's just that DO doesn't know how at this point and time to make a sequel that's not repetitive.