This means there will be a glut of Java devs and lower rates though as a consequence doesn't it?
But in theory, in 10-20 years any widely used programming language will have no intrinsic value and will have enough developers to not pay them 6-figure salaries.
Developers that will be valued and making tons of money in 10 years will be domain-specific developers.
I guess the question is more about what still will be in high demand in the future and takes a very long time to learn or has other barriers, so there will be effectively no competition.