Specifically, I'm thinking of separating its UI and from its
diagnostics-generating backends. Currently the latter rely purely on
lanching external processes and examining their output, but recent
experimentations with the LSP (Language Server Protocol) showed that to
not always be the case. Another example is Elisp itself, which is
syntax-checkable without an external tool.
If you are thinking: "Hasn't flycheck.el done all those things
already", the answer is probably yes, but flycheck has been around for
some time and isn't in Emacs, whereas flymake.el is. Anyway, that is a
whole different topic. I believe flymake.el's flaws can be fixed and it
can be made as good as, if not better than, flycheck.el.
I'm also committed to maintaining backward compatibility with the many
flymake.el configurations out in the wild.