Japan might be able to improve. In recent years, there seems to be an increasing willingness of their top players to head overseas and play in more competitive leagues. This season, their mens national team has six players players abroad (EBEL, VHL/KHL, ECHL, AlpsHL, and Poland), which appears to a record number of domestic pro players playing outside of the Asia League. Last year and the previous year, their U20 team also had 6-7 players playing abroad. At least that's some hopeful signs that the Japanese Hockey Federation is recognizing, or at least will soon wake up to realize, that Japan needs to improve its development systems if it wants to improve its international standing.
South Korea is on a different path though. It will likely take multiple decades before ice hockey makes in-roads there. Korea seems to be where Japan's system was twenty years ago. They have more or less maintained their IIHF ranking since 2018, but it doesn't look like they've been able to maintain any of the development success that they experienced leading up to the Seoul olympics. Since then, they've folded two of their three Asia League teams, they haven't grown the number of registered men's players (still around 130 registered), all of their national team "stars" are 30+ years old, and success of their U18/U20 teams has been stagnant.
On the bright side, they have Jim Paek coaching their international teams and Asia League team, and quite a large number of ice rinks (according to IIHF). On the other hand, their player base is a fraction of the size of neighboring Japan and China, they have an even less cultural connection to ice hockey than Japan (and China to a lesser extent), and Korean youth seem to have more external pressures that drive them away from sports than in Japan and China. IMO, South Korea needs to focus on making ice hockey more appealing to their youth and increase player registration before major improvements to their development systems will be useful. The state of ice hockey in South Korea will likely get worse before it gets better.