Korean work culture is so awful I'm not sure they could even find enough foreigners willing to work like this long-term. Also the language is really hard to learn.
The only solution IMO would be a culture change. But this is not going to happen while old people hold the reins everywhere.
I think people are talking about immigration, though it's a thorny issue, partly because Korea has been virtually monoethnic for a very long time. But I think Korea will eventually have to open up more: the current population crisis is so dire that I don't think Korea is in a position to choose its medicine.
(I don't think immigration alone will solve the problem, BTW - Korea should obviously fix its horrendous work culture, education, and runaway housing prices.)
I think part of it is, as the youth numbers decline, the culture declines with it. This is addressed in the video, people >18 and <40 are those who keep traditions and culture alive. If you somehow imported a bunch of babies who were raised in Korean families, Korean culture survives, and if you import a bunch of 60+ people, well they're not going to be spreading their culture as much as someone who is 30. But babies and the elderly aren't the ones immigrating all that much, it's the (relatively) young singles and families. If you somehow managed to keep up the current population of SK by importing only young Thai families, within 4 generations SK would be North Thailand. I think is only a small part of why many countries are resistant to immigration, and on the micro-level, it's as simple as asking, do you want more neighbors? Or less? And I think, generalizing greatly, most people would say less.
The only solution IMO would be a culture change. But this is not going to happen while old people hold the reins everywhere.