Yeah I mean, if everyone has a Digimon partner, that kind of takes the air out of being a "Chosen Child", right? Maybe Digivices stop proliferating to children as more and more partner with a Digimon... There's not really a need to be Chosen anymore if everyone has a partner.
Without Digivices, there's no reliable way to evolve your partner, so maybe Digimon evolve at the pace they would normally, without a Chosen to share energy with. That probably means that very few people see their partner evolve past Adult, with an exceptional few getting to Perfect and even Ultimate. Those cases are so few and far between that in the event that a human-Digimon partnership decide to use their powers for evil, there are systems in place to keep them in check.