If you were going to do this, I'd advise you to make a list of [general] spells that all wizards get access to. if I recall, in 2e, they were broken down into abjuration[general] or universal or whatever.
So, spells with general utility, like detect magic, mage armour and a few other staples are tagged on the Universal list. You used to get 2 extra spells that were part of your specialization so those [universal] spells, if they are also part of your specialty, could be taken as your bonus spells.
Honestly, the balance of schools was never equal. Even the old way of specializing where you had to drop one school to become a specialist in another one wasn't ideal. It was never as good to be an illusionist as it was to be an invoker because so many creatures were immune to illusions.
In any case, I like the idea of dividing wizard-types into their schools and restricting them somewhat based on what school they are. I was going to make a project of dividing the spells into balanced schools. But I'm lazy.