The problem isn't the overall demand for developers. The issue is that AI will replace entry-level developers, thus eventually reducing the ranks of experienced developers. A senior developer brings much more to bear on her work than simply coding skills. Where is she going to get that experience?
That is a real problem indeed. It is the same problem though. Obviously the developers that will get hired to do the 10% need to be developers with a lot of experience but as you say where you are we going to find these people if the overall number of experienced personal has dropped?