I see this as an opportunity to confirm behavior of external links in general...
The current RCE seems to know when an outside resource is being linked and generate the appropriate target...it takes a refresh of the page once inserted and saved, but I can confirm that it pops it open in a new tab/window.
The new RCE has a specific path to follow as is currently constituted in beta. When you go to insert a link of any sort you get two paths to follow...External Links and Course Links:

Inserting the External link seems to do the trick right away without a page refresh.
So it would seem that the CTRL+K shortcut only serves as a stop-gap to provide assurance that your external link won't replace the learning environment with your resource without having to dig into the HTML code and insert target="_blank" to the <a> tag. I didn't even know the keyboard shortcut was an option until about a year ago and then started using it religiously. Since I'm the one that asked the question that resulted in "cricket noises", I assumed I asked it in the wrong place. I'm used to content management systems like Drupal and Wordpress that push the choice right in front of you so I thought it would be nice if the RCE followed suit.
Maybe it's not such an issue after all?