It'd be cool if Legends adds a plot where the Machop/Machokes, Geodudes/Gravelers, and Meditites/Medichams that make up over half the routes in Sinnoh were introduced from other regions. This could be the reason why the snowiest region has the fewest Ice-types and the Platinum Ice-types like Swinub and Snovers are found in the underground in BDSP (i.e. they went into hiding) or only available by Pokeradar/Swarm in DP. I always found it strange how the Battle Area has so many different Pokemon on every route despite being so small but Sinnoh has so few.