With all due respect, this seems contentious and unsupported. I don't
see any particular reason to believe that a tool for the coherent
maintenance of a long-running image would also be a good fit for more
conventional development.

You do not see it, but there other users out there that do. I do not need to keep my image up and runnign throughout my development process and I can still achieve the same thing. I am not disputing your development model, I am disputing that anyone wishes to impose anything like that on anybody else.

There are already tools for the non-image-driven development. If ECL is
not aiming at image-driven development, maybe a tool like make, or make
+ autoconf would be a better fit.

I do not see why and how. Compiling lisp systems can only be done from lisp environments. This is not like you write "ecl my-file.lisp" and get something else precisely because that lisp file depends on a lot of other things.

That said, if you wish to try to make ASDF work for conventional
build-and-exit system construction, and that doesn't break ASDF for
image integrity maintenance, more power to you!