I think it has nothing to do with weight, as a statement about Anko or women. Anko was just one more victim of Kishimoto's ending theme of not giving anyone the ending they wanted.
Yeah, there's definitely overtones of mocking. Since there don't seem to be any heavy females in the manga then yeah, her obvious weight gain stands out. However, Kishimoto likes boob jokes, pissing, farting and potty humor. A lot. So really, the bar's not set very high.
But the way I see it, she's just one more character Kishi can screw over in the end.
The ending really was not about a fulfillment of goals, but about how reality is harsh. None of the characters are happy or fulfilled. Anko is just another one.
And why fat? She was also sexy so she could have been shown as paired with a dorky shinobi. She was fierce, so she could have been shown as weak. Any of those opposites would've worked. I think the fat joke was the low-hanging fruit for someone who's really grown to hate his work.
What bothers me the most is why was she even shown at all? She was only ever a plot device. She might have been a memorable character from Part 1, but her momentum in the story has long since fallen away.
Why not show a panel of Yamato pulling himself out of the wreckage, squinting and smiling up into a ray of sunlight? He was infinitely more beloved and important to the plot.
And who frickin' cares about Anko? If she weren't shown in the epilogue, NO ONE would be missing her. Unlike poor Yamato.
Which is why as many of us have said, Tricksie,w e just got an ending. NOT A HAPPY ONE, NOT THE ONE WE DESERVED. JUST A DAMN ENDING.