I checked the search function and I found a similar topic but the thread (involving world openness) made me think of another question.
In this region I know we will be able to travel all around, although levels of other NPC and encountered pokemon may influence us otherwise. But in turn it made me think about gym order. Between the 17 gyms, will we have to go through a set order?: to get to gym "B" we have to defeat gym "A" first? I know like most of the games some areas will need to be unlocked by using certain moves or HM's to travel to the next area or you can proceed to the gym but a sprite blocks the entrance to the next gym. However, what if you could choose a path to gyms "A" "B" or "C" and complete those in any order, for example. Then a certain item or move or HM or quest takes us to the next area where we could complete gyms "D" "E" "F" and "G" or something like that.

Not trying to dive into gameplay, but just checking if there could be a feature like that or if the mapping would be pretty much straight forward. I know I read somewhere that Miryus would definitely have a series of islands but I obviously don't know how much the islands influence gym placement.