The traditional definition of an "illness", I think, is something that would cause you pain even if you were stuck on a desert island
Good point. Not having any good video games is definitely an illness. As is not having food and not being immortal.
Not being immortal (in the sense of dying from old age) is obviously an illness, but hasn't been recognized as such by most outside the transhumanist community, because it's universal. It would be in a sane society, but there you go.
Nutrient deficiency of various sorts has always been recognized as an illness (eg., scurvy for lack of vitamin C), and this has since been expanded to include general starvation (ICD-10 code T73.0).
Lack of video games is a fact about the video games, not a fact about your body.
There was some talk here about height taxes, but there's a better solution - redefine shortness as a treatable condition and use HGH to cure it. They even got FDA on board with that, at least for 1.2% shortest people.
Unsatisfactory sexual performance became a treatable condition with Viagra. Depression and hyperactivity became treatable conditions with SSRIs. Being ugly is already almost considered a treatable condition, at least one can get that impression from cosmetic surgery ads. Being overweight is universally considered an illness, even though we don't have too many effective treatment options (surgery is unpopular, and effective drugs like fen-phen and ECA are not officially prescribed any more). If we ever figure out how to increase IQ, you can be certain low IQ will be considered a treatable condition too. Almost everything undesirable gets redefined as an illness as soon as an effective way to fix it is developed.
I welcome these changes. Yes, redefining large parts of normal human variability as illness is a lie, but if that's what society needs to work around its taboos against human enhancement, so be it.