In reply to Jared Zimmerman (WMF) from comment #31)
> Its relevant because asking for feedback on "the usual channels" completely
> omits the target user, when the target users is a reader. Jon's point that
> we can do it and then iterate speaks to the fact that it is one of our only
> ways to get reader feedback. To roll the change out publicly then iterate.
> We can get better at this eventually, but at the current juncture, I think
> this is a sound plan based on our infrastructure for eliciting feedback from
> readers and others who aren't aware of, or participate in "the usual
> channels"

I would think that 'users' here would include readers and editors both, and even then, editors often know their readers better than one might expect (such as by talking to them, or being them). So talking to the editors is probably exactly the right place to start. They could tell you things like the fact that some of these external link styles, such as IRC, will never appear in article space (on a non-technical project, anyway - mw.org or archwiki and similar probably have quite a few irc links in various articles), but are often used in project and user space (so changes to that style would be purely editor-facing on projects like Wikipedia, not reader). Or that readers often complain when <blah> or have trouble with <blah>.

And there is also ample infrastructure in place to test potential changes, is there not? For instance you could do:
* A/B tests to determine if readers are less likely to click on external if they are or aren't visibly marked as whatever kind of link they are. 
* Scripted tests on usertesting.com to gain insight into possible reactions to unexpected pdfs, audio files, IRC links, etc vs regular external links, and to the external link icons themselves when they are used, such as if they even figure out what they mean.
* A betafeature for users to see if removing the special icons affects their workflows, or if they prefer it outright.

If there is a problem, you should be able to prove it without just deploying it first and asking questions later. Also what Derk-Jan said.