Well, your ideas may somewhat be a little realistic, but let's face the facts, they are not cool. No one wants to see a devil fruit user who's only ability is to grow old. The DF-object transfussion has not been explained yet, but sooner or later may be explained. As for why no one gets a negative effect from DF's, it's because they already have one, the inability to swim. It's basically a balance, you become strong and at the same time become a hammer. And DF users have so many weaknesses. As for the anti-DF, that's what seastones are for.