Worst case scenario is mid tier below Japanese games move on from their systems which is either something that'll take a long time or won't happen because they're mid tier and below and need all the sales they can get.
Most likely these devs will just apply wholesale censorship to their content which will affect all platforms which is what I'm guessing is what Sony wants here.
The vita was king of these games and was one of the lowest selling handhelds both in and out of Japan so not much
It's not going to kill PS5 overnight or anything but I feel like it shouldn't be underestimated just how much Sony platforms have benefited from the being the default platform for 99% of Japanese third party games for the last 20 years. Intentionally loosening that grip is absolutely something that could hurt them in the long run.