When Selebus started work on the game, he had two conflicting ideas of what the game would be, and he felt that the game had to have H content early on to generate interest. So some of the girls rush into their H scenes with barely any setup, which is especially jarring two years in and every other girl is moving at a much slower pace.
So he's going through the early game to slow things down a bit. Ayane, Futaba, and Makoto are going to get more buildup before they start fooling around with Sensei. The Ayane bathroom scene is being removed entirely. All told, some 158 scenes are getting altered in some way, though some of them will be very minor.
This won't break any saves or change the plot, so you won't need to replay the game unless you want to, but it will halt forward development of new updates until its done (target date is 6/1, though he did say it could potentially take up to a month longer).