> In general, given behavior that is old enough, you can be sure that someone, somewhere relies on it.
Is it a documented API? If it is, it is probably the worst "API" in the history of software and should be deprecated and removed. If it's not, just remove it and be done with it. If you rely on that sort of output, it's really your own fault and people can change their code.
I really really hate that Emacs prints messages when it really shouldn't. But I can live with that, as long as there is a way to turn them off, which there obviously isn't now. The non optional output is sort of a blocker for me as well.