Well I mean Noxus still has huge incentive to take over Demacia considering how resource rich their lands are comparatively to the empire's, but Noxus also has other things to consider, such as potentially re-invading Ionia with different strategies, taking over more of the Southern Continent, potentially taking over Piltover, getting more of a handle on this whole "hextech" business, etc, so it's not like that conflict is the defacto storyling for Noxus anymore when it comes to interacting with other nations.
Just because Demacia's sticking to itself doesn't mean it's devoid of interaction with other areas of the world. I mean Ionia was that for ages and now look at it; enemies with Noxus, kind interested in Piltover and their hextech, presumably got Bilgewater pirates to deal with, etc. Demacia's at least gonna have Freljordians to compliment the Noxian attacks.
There's probably a lot more internal struggle in Demacia atm considering how the champions are. We see folks like Taric and Jarvan showcasing a different kind of thought process that's counter to Demacia's dogmatic traditions and policies, and you've got champions within Demacia that by their very nature question their conventional thinking, such as Lux, Poppy, Galio, Sona, Shyvana, Quinn, potentially Xin Zhao, etc. I mean let's look at that for a second:
- Lux is a sorceress noble in a society that sorta distrusts magic
- Poppy's a yordle, something that Demacians are probably very wary about and yet she embodies the things they exemplify
- Galio was made by them, holds their beliefs but is also magic and inhuman, something that likely worries Demacians
- Sona's a noblewoman who is also potentially innately magical and an immigrant, and even without being innately magical she has an incredibly potent magical instrument, so who knows what's going on with her
- Shyvana's a confidant of the prince and would be seen by many as a monster
- Quinn's was born in the sticks and yet serves directly under (or close to this) Jarvan IV, which likely made some folks shake their heads
- Xin Zhao's an immigrant too, though of unknown origin, and yet became seneschal of Demacia's monarchy.
I feel like Demacia's got a lot of potential thinking to do about how it considers itself and its place in the world. For that reason I'd say J4's perhaps the most important character in the overall Demacia narrative at the moment, if this line of thinking has anything going for it. I'd say that's a pretty interesting story.
tl;dr Demacia's a nation of folks wary about magic and insular, but also has magical folks and immigrants within their aristocracy, has magical beings guarding its borders and has its prince having good friend in what amounts to a peasant girl and a half bred monster. A lot of story potential there.