I actually do believe that manjuu has an Azur Lane succesor in the works, be it a full sequel or a spiritual succesor with plane girls. But it simply doesn't make sense to announce it now. First, because they're trying to diversify their portfolio with an ambitious game like Promilian. Second, because Azur Lane is still ""stable"" and they know the minute a sequel is announced, players will start panicking about EoS and reduce spending. In the meantime, they're experimenting with stuff that could make it into the sequel like the 3D Chibi farm, TB raising sim and the 3D dorm.

If I had to take a guess, AL2 or Azur Welkin or whatever will be announced by the time Promilia is 2 years old ish, and when Azur Lane is in it's 10th anni. Then, they two games might coexist for a few years much like GFL and GFL2 do, before they gently pull the plug on AL.

The sex fanservice is simply them trying to remain competitive in the waifuge market. AL has naturally shrinked with time and doing the chaster Waifu fanservice from before won't get them the buzz it used to. It's a shame to see stuff like the loss of lolis, the breast augments, or some ships getting absurd preferential treatment, but it is what it is.