Planetside 2 is exactly what this sort of reminded me of. In PS2, you can have over 1k players within an entire continent, which is a seamless quilt of many zones, each of which can have up to several hundred players (north of 250 is the most ive seen). The beauty of it being that there is no delineation between areas for players, but clearly the servers are somehow breaking down the continent in some way. So you can have a single battle raging across 2 adjacent areas with 96+ vs 96+, with the perception of being on a single battlefield.