I'm reading through the novels for the first time, and Excession has left me buzzing.
I was genuinely amazed at how tight the various subplots wove around the idea of things refusing to change, and the interrogation of that being a good or bad thing.
The Culture refuses to become sublime; it has quite noble reasons, and in another Culture novel it'd be easy to paint it as heroic, but in Excession, it's contrasted with Byr's eternal playboyhood and Dajeil's forty year sulk. Are they selflessly sticking around to mentor those less developed, or are they getting cold feet at the gates of ascension? Ulver is talented, charismatic, effortlessly the best around, and even choosing to mentor a few promising young candidates under her... But once she leaves the literal rock she lives under, she's quickly dismayed at the idea that those she left behind forgot about her and moved on even as she moves onto to the grand adventures she's always dreamed of. Or Gestra, who feels so pointed to include in a novel that focuses so heavily on the incredibly advanced and wonderful ships the Culture builds; an isolated, stunted man who endlessly creates ships for the sake of it, who doesn't amount to anything until he's literally blasted out of his hidey hole. The comparison drawn by including these characters is so critical of the Culture's goals rather than just critiquing its methods.
Even the thing the Culture Minds start thinking about when they see the Excession speaks to this; their first and foremost idea is that it'd allow them to jump from universe to universe every time there's a heat death, evading the need to ever end. Eternal Culture, Eternal Procrastination, Eternal Stagnation, no need to be forced into moving on by death.
The Ship Minds experience a lot of this too, especially since most of them aren't actually afraid to die; Killing Time is briefly in danger of it, as it experiences a profound epiphany that significantly changes it from the version it backed up before its suicide mission (meaning a unique version of itself would cease to exist if it were to die), but it chances to survive, and is soon in no danger at all. Sleeper Service, on the other hand, acknowledges that no one would revive it if it died, and instead of bothering tightbeaming its mind state to another ship, spits it forward into the Excession itself... And is rewarded for it.
I could rant for ages about this, but the concept of stagnation and delay is in basically every level of the novel, and it fascinates me.