I think it's important to distinguish between fat admiration and feederism. I'm sure that fat admiration will become more and more accepted... in many ways it's already pretty mainstream. There are songs about it, and it's generally acceptable for a guy to "dig fat chicks" even if he might get a bit of stick for it. I imagine it's probably harder being fat, but then increasingly you'd have the weight of numbers on your side (pun clearly intended!).
Feederism is altogether different, though. Some fetishes are always likely to be seen as rather dark, and I suspect feederism will fall in this category. A fetish doesn't have to be understood to be accepted - I don't get foot fetishes, for example - but it does need to be seen as benign. Feederism is seen as inherently destructive - after all, fat is bad for your health, apparently.
Yes, there are misconceptions of control, manipulation and mental illness which cloud the matter too. But ultimately I think the fact that gaining weight can be bad for health, particularly when combined with the common preference for extreme unfitness, will keep feederism from ever being truly accepted. Heck, I have the fetish and still struggle with this issue, so heaven knows how someone who can't experience it will come to accept it.
12 years