I never thought of this because I'm a chronic "middle-clicker" (I use separate tabs for sooooooooooo many things that 99.99% of people never do), but I just realized today after not having visited for like half a decade that standard left-clicking on a chapter link actually just opens it within the same tab. This got me thinking - considering that the story map is like an index, wouldn't it actually make more sense if it instead open chapter links in a new tab? For example, I like to always have the story map open when reading, often times jumping around to chapters written by a specific author.
Hmm. I see where you're coming from, but I don't like it. It takes away choice. Right now, if you left click, you open in this tab, and if you middle click (which, like you, I do often) it opens in a new tab. But with target="_blank", we no longer have a choice whether to open a link in this or a new tab. And I'd like to keep that ability, because there are situations in which I don't want to open in a new tab, for example if a chapter only has 1 next chapter or when I'm in game mode or when only 1 of the options interests me.
I usually open everything in a new chapter. Still, I think that doing it automatically might feel rather intrusive.