You know, I think we're missing the real story here.
We all know people will never stop proposing "it isn't technically incest since the MC hasn't had sex with Jill yet" theories. Clearly, the only way to end the madness once and for all is for the MC to have sex with Jill.
Thus we, the audience, are ourselves motivated for this outcome just as the young, horny MC is. It drives home the same uncontrollable eagerness and anxiety our avatar is feeling as he pursues his dream girl. When you think about it, it's a stroke of meta-brilliance.
That, or the internet is a cesspool of crazy fetishes that will never die. But that would just be too depressing if it were true.
In all seriousness, how would this be any different than Rusty becoming pals with the MC because he likes and respects him? That's already well on the way to happening without and Burgmeister blood, so it seems like much ado about nothing.