I don't think Disney movies about mermaids, sea-creatures or ghost-pirates will automatically lead to more sales for Playmobil in those themes.
Children will want the actual Disney merchandise with figures that look like the ones in the movies, right?
In my view, basics will always do well: houses & city-life, police force, the school, trains, knights and castles...
But if the theme gets too crazy (i.e. Inca caves with green aliens) or too specialised I guess it will sell less.