I was a little bit surprised by the way spell specialization works. I guess I do still think there should be options to specialize in a specific casting Skill - to be a Diviner, Conjurer, Abjurer, or Apporter, and gain some benefit from that.
But I am very, very surprised at how happy I am with the way the Arcane Knowledges were built in, and I quite like the way the specializations in them do work. And if your players want something from outside their list, they can always learn an Esoteric Spell. Thematically, the idea that you can be specialized in, say, Elemental magic, but you can freely learn any other kind of magic and it's just that you only get this bonus with Elemental spells, doesn't feel right. And the lists they give really are pretty effective - especially considering how much we all gripe about how hard it is to ever get a lot of spells, each of those really gives you a pretty big list to work from.
The idea was that we already have a benefit for specializing in a single magic skill in that you can take the big spells faster. Anything beyond that can be done in Year Two when we can justify having lists include spells that don't have immediate game impact.
But one of my goals with the spell lists was to make sure everyone had a decent selection of spells no matter which specialty they chose, so I am glad it worked out that way.