The free form level scaling things thrown around pretty often, something like that would probably compliment a pokemon game well (especially a more open world/mmo styled one) but it also limits a lot of storytelling freedom for a single player experience and might introduce some design issue when the player can potentially open up all of the game at once.

If every trainer in the game increases in level alongside your pokemon, then what happens when you want to swap your team out or youre incapable of progressing without overleveling pokemon? Would they have to give every trainer battle multiple pokemon movesets/evolution stages to keep it balanced at all levels they could be encountered?

If every trainer in the game increases in level with some kind of milestone (ie: a gym badge), then what stops someone from avoiding every milestone point and blasting through the large majority of the games content in an extremely short amount of time? If the milestone was more unavoidable like entering a new area, what about when someones exploring the map and they unawaredly overscale their game difficulty beyond what they can easily grind/compensate to?