Hello Sersus,
with vector maps, I don't see a problem. Locus has auto-loading feature (in settings > maps - advanced), so vector maps should be correctly auto-loaded when needed.
With GraphHopper is one major problem. Currently it do not allow to compute route over more files at once. This is, next to few other issues, one reason why it cannot be now a public add-on and still remain in Beta.
So for now, it's not possible to make these areas bigger, because we improved our generator for Vector maps, so for same areas as vector maps are also generate areas for a GraphHopper.