Your thesis seems a bit hard to explain... It bounces between two things. First, story arcs are being cut off faster (hence the quick reboots). But then, story arcs are being extended across a show's entire run. These seem at odds. The first one is due to a shorter attention span, but the second one requires a longer one. The goal of both seem to be real character change, so that makes sense, but relating it to attention span (or 'accelerated culture') only makes sense for faster reboots. An accelerated culture values grab-and-go type things. A show with a huge story arc is inaccessible to people who are not willing to sit for hours and make up for lost time. I don't see how that willingness to wait week after week and/or the willingness to make up for lost time has anything to do with complicity to an accelerated culture.
A good point; see above for a distinction on a genuine arc and a narrative bookending.
Regarding attention spans: you're right, the two push in different directions. But it's the same force pulling on both sides! A demand for immediacy in seeing the new episodes
now, versus the demand for being able to see another episode immediately after the previous one, which you only get by waiting. It's just a matter of which type of attention span gratification you value more.
That said, I think the delivery of the entertainment gets around the problem a bit. Specifically, the fact that lots of people deliberately consume these shows all at once. I've heard from lots of people who deliberately let shows build up a store of episodes before diving into them, which has the added benefit of having to worry that a show will be prematurely cancelled, too (a huge deal with serialized shows). There's enough out there now that people can consume these things at a tremendous pace, and yet still be pretty selective about narrative moment, without running out of options. It can't go on forever, but given the number of options it can go on for a pretty long time. Courtney and I, for example, have been making our way through lots of the great shows of the last decade for a couple of years now, and we're still not through the standard dozen or so that form the consensus top tier.
In general, it seems weird to me that an 'accelerated culture' would cause that kind of shift. The real cause still seems mysterious to me, but I think it's closer to something like your idea of wanting 'real change' than 'grittiness/realism.'
It could just be contradictory, in that being impatient means we want things faster, but that means they run out quicker, which makes us more impatient. It would hardly be the first human desire to find that trying to satiate it only makes the desire worse, no? It can work as an explanation for the shift, even if the shift is unsustainable in the long-run.
Also, I'd just like to say that the James Bond example above all is really great, because that has such a long history of being totally stagnant.
Yeah, it's pretty much Exhibit A, especially now that they've tried to change it. Pretty sure that's going to fade and we'll only have "arcs" that involve a few movies with an over-arching shadowy organization, maybe, without a lot of psychological change from Bond himself, but we'll see.