you can transport to dream world and in dream world you can take ship to johto kanto(hgss version) and bw2.transport out of dream world you can go to the maps like nowadays
Johto and hidden ability have been delayed for a long time,since one of possible reasons is the difficulties of dealing with double kanto maps.Why don't we count both HGSS maps as dream world,the very place which players can get hidden ability pokemon?