A lot of people have migrated away from Java to better JVM languages. If Java actually keeps improving, there's a reasonable likelihood that people will stop migrating and those that have may come back to Java from these other langs.

Long term this could lead to a loss of maintenance for tools and libraries for these languages which could kill them and leave those that migrated with a dead & decaying ecosystem.

Of course this is a bit of a stretch but it's not unheard of.