I am afraid that the middle class in (some) developed countries will eventually self-destruct. While immigrant intermarriages could help mitigate the effects, it gets complicated not only by class and ethnicity but also the number of people willing to start families with children. Children are inevitably the next generation of adults.
Without a substantial number of children, some countries might (and will) not have enough of them growing into adulthood to supply for the next generation’s jobs. Should childbirths decline any further, there might not be enough people to be hired for dog breeding. Immigrants could help but that still depends on each one if we take them as individuals into account.
Like I said, if there’s a shrinking number of breeders people would have to contend with skyrocketing stray dog populations instead. While this is complicated in practise, it’s going to turn out that way for whatever reason and circumstance.