It will be a modest hit in Japan, and I'll elaborate a bit for the West. Japanese, out of drawn smut, aren't really asking for more fat chicks; it is a fetish and there have been a couple of these characters, but they're not consuming it. It's seen more as a fetish than something outright desirable. Idols, actresses, singers, you won't really see a lot of them being overweight, where even weighing 5 kg can make them get greatly upset. If the writing and comedy is well-executed, it could be bigger, because at least they insult each other based on their fatness, which brings me to the West.
I can't say for certain if it'll be big in the long term. They'll go crazy because "thicc" women, but the usual suspects will quickly turn on the series, because it doesn't promote this lifestyle as healthy. The girls get gassed when doing just a bit of exercise, are always bouncing back into fatasses, they insult each other based on this fatness, and it is ultimately taken as both comedy and fanservice; it is not a desperate plea to accept being overweight and unhealthy, and the girls are always desiring being more slender, though they have their weakness for food or other bad habits.
tl;dr It will be big in the West, but expect vocal viewers to quickly turn on it. Others will watch it to fap at fat chicks.