The USA qualified for the last world cup by playing in the USA against SA and Jamaica using mostly home grown players from their domestic league, which has grown since then. They can do it again. Once they qualified they did indeed pick a team of ex pat Americans and ditched some of their domestic players who helped them qualify but I think the team that did play all had as bona fide American connections or American passports.
Italy also qualified by playing in Italy and barely defeated a Lebanon side to qualify on points difference I think. As with the USA the Italian League is growing. The use of heritage players to get a good performance at the WC was great publicity for the game in each country which must have enhanced the knowledge and interest in the game.