How can I elaborate on answer that I don't have?
Self-application is an important form of scientific methodology. Think e.g. of programming languages development: one of the first things you do is bootstrap a compiler.
PL research is a discipline with no really feasible empirical methods for robust and replicable evaluation of programming language ideas. Using self-application is a test of internal coherence -- if your new language is not good at writing a compiler, then maybe it isn't such a good idea.
Self-application is a well-known scientific methodology. Would you trust a physical theory that predicted the impossibility of physicists?