I wouldn't be so sure. Aevium has a lot of hidden and uncharted areas not on the map. for example, that whole garufa temple under carotos mountain xen base, or the Sheridan Wetlands. We also have the entirety of Neverwinter island left to explore, we don't knwo how big it is because it isn't on the town map yet. We also don't know how much of Past Aevium we still have to explore, or if we will explore more eras via time stone. Or even GDC for that matter, we still have an entire university to explore, and most of the underground is currently blocked off by team bladestar. HM waterfall will open up more areas (many areas have waterfalls you can reach by surfing, but you can't go up because you need Waterfall.) Remember how many not-only-unseen-but-not-even-alluded-to areas HM Dive opened up? I'm pretty sure there a LOT left to explore, despite the map seemingly being almost filled.