Under current RAW, specializations/expertises explicitly are dicepool modifiers, not skill modifiers like Reflex Recorders and Improved Ability.
Under the hinted likely errata, the +4 limit will be on dicepool modifiers, while specializations/expertises will explicitly be converted into skill-bonuses and thus not count for the +4 limit. In other words, under the changed system, a Force 6 Spell Focus would only give you a +4, while the Expertise Spellcasting would still stack at +3 for a total +7. But until the final errata come out, we don't know for sure yet if this will all be in there.