An increase in the level cap in combination with new content to go with it (new zones to explore etc.) would work.
If all that's done is add another continent, with new skins on the same mobs at the same levels, all the people now complaining about the lack of content would have maybe a day before they're bored exploring it, at most another 2-3 weeks before they're bored of camping the bosses there.
It'd not be a challenge to them. New clothed ditto. People will try them for a week or so, settle on a style (just as they do now with the choices we have, which imo aren't overall bad at all), and complain that there's no new content.
If all that's done is add another continent, with new skins on the same mobs at the same levels, all the people now complaining about the lack of content would have maybe a day before they're bored exploring it, at most another 2-3 weeks before they're bored of camping the bosses there.
It'd not be a challenge to them. New clothed ditto. People will try them for a week or so, settle on a style (just as they do now with the choices we have, which imo aren't overall bad at all), and complain that there's no new content.