You paint the problem as being about us adapting to changing demographics. I'm not so sure--if only because the notion of attention-impaired millennials appears to be one of those self-propagating ideas whose supposed statistical support turns out to be fabricated.[1][2] If the concern is about getting more _readers_, by providing a digestible version of articles, Google already attempts to do that, and I'm sure we'll see better efforts down the line.
I think the bigger problem, and I'm not breaking any new ground here, is that our vectors for bringing people into the editing fold may be shrinking. Short versions of articles, whether we provide them or Google does, do not readily lend themselves to participation by outsiders. Mobile devices are inherently challenging to edit with: the WMF rightly has great people working to make it easier, but at the end of the day, I don't know if I would have ever started editing if I'd had to do it on a phone. (I hope my millennial brethren are hardier than I am.) And, as Frederick notes, even if someone gets to the point of editing, finding sources that we consider acceptable is going to be hardest for the areas in which we're most lacking coverage. These are hard problems, and I don't claim to have the solutions, but I don't know if your proposals would help on this front.
In any event, "slowly d[ying]" doesn't quite seem "imminent". Call it a side issue, but I'd prefer not to be clickbaited on this list.
Emufarmers, editor, a few edits
[1] https://www.bbc.com/news/health-38896790 [2] There's gotta be some Person's Law I can cite here, right?