Yes HeroEngine does. Our Seamless 2 technology allows you to create seamless open world environments. With HeroEngine there is no world size limits. Instead of how other engines handle open worlds, we limit area (zone/levels/chunks) size instead with upto 1200 square meters. Your game design and scope will termin the restrictions for area size. Most MMO's area size range between 250 to 512 square.
More information about HeroEngine's Seamless 2.0