Adding tanks with Scene and Story to a game that lacks somewhere around 70% of that content for existing tanks and then taking her away again, is a really odd way to do things.

That she is a busty nice looking girl with, what is from the looks of it on the Nutaku page, a good scene, is rubbing it in real good too.

It'd make sense if the other tanks had adult content, yes, but they don't. So being in that situation, what is the purpose of limiting the content that the game do add?

To illustrate the perplexing choices being made here,

2 adult scenes added in 7 (8?) weeks for girls without one, rest of production has gone to new or time limited girls I believe?
For the sake of illustrating it, lets randomly say that around, 80 out of 110 girls are missing adult content?

So that's 80 girls, at 2 scenes pr. 7 weeks = 80 * 7 / 2 = 280 weeks at current rate to reach full coverage. So almost 5½ years to go.

Lets ignore the lower star girls and assume they simply get stories and that the 3 star is where it begins. Think that is 30 girls.
So (80 - 30) * 7 / 2 = 175 weeks or 3+ years.

Dropping the 3 star too, that's another, let just say 20 girls for nice numbers to work with.
So (80 - 30 - 20) * 7 / 2 = 105 weeks or 2 years (for existing 4 and 5 star girls alone).

No Sir, time limited or gated is not the way to go here.