Both Eldritch Knights (a subclass of fighters) and Arcane Tricksters (a subclass of rogues) pull their spells from the wizard spell list, albeit in a limited way. The way in which they do this is by only being allowed to choose spells from the evocation and abjuration schools, in the case of eldritch knights, or from only choosing from illusion and enchantment, in the case of arcane tricksters. Both classes also get very small amounts of any spell they want from the wizard spell list.
How unbalanced would it be to allow both these subclasses to choose spells regardless of school from the wizard spell list? Good comparisons may include comparisons to half casters, and of course to changes in how these classes could play.