I have to say it's a bad thing for these nations to compete together in men's artistic gymnastics. I'll try to explain in detail.
First, The 2012 Olympic vault champion is from South Korea, the 2016 Olympic vault champion is from North Korea. These gymnasts work great as individuals, but they could never compete together in the same team. At the 2020 Olympics, teams will be composed of four gymnasts, and these gymnasts have to perform 18 routines during the qualification stage: 2 gymnasts will perform 6 routines, and 2 other gymnasts will need to perform on three apparatus each. Vault specialists perform usually on one apparatus: vault (or maybe two, vault and floor) and it's virtually impossible for a team to have two vault specialists if they only perform on vault (or vault and floor).
Second: there's a chance we can have one gymnast from and two gymnasts from competing in vault finals at the 2019 World Championships. I'd say there's a 10% chance for this to happen, but 10% still beats zero. However, If they compete in the same team, only 2 gymnasts per nation can advance to the finals, so one of them will have to sit out, which is bad for these nations.
Third: has a real chance to qualify 4 gymnasts in a team and 1 gymnast as a specialist, and has the chance to qualify 1 gymnast as a specialist. The thing is: both and could qualify 1 gymnast each as a specialist, but if they join forces, they would only be able to qualify 1 specialist (I mean, there's still, technically, a chance for them to qualify 2 specialists, but this would be a lot harder if they work together instead of competing separately).
It would slightly make a difference in women's artistic gymnastics, though. If North and South Korea join forces, they could realistically try to qualify a full women's team since major nations like Romania and Germany are struggling with their women's programs and will have trouble qualifying a full team for the 2020 Olympics. The problem for Korea is that there are many programs on the rise, especially Brazil, France, the Netherlands and Argentina.