It wasn't gonna be an ending that would please everyone. Obviously going for a "kiss the loli" ending wasn't gonna happen, because it pretty much goes against all of Mimika's development. And thinking about it, going for the "you're 18 now, you know what that means" ending would probably be awkward for other reasons (mainly that none of you dorks can probably even picture what an 18-year-old Yuzumori would look like). This is a pretty fitting ending that emphasises the romantic aspect rather than the lewd aspect.
Either way, there'll probably be more content in the fifth tank coming out in May.