I think Arcane Barrage should still receive the 20% chance to proc Missle Barrage regardless if Missile Barrage is equipped or not. This would free up the options to use Spellfrost bolt as an alternative to Arcane blast and free up some new and innovative dual spec possibilities.
Sure, you’d only have a 20% chance, but now you can take other abilities as well such as Ice Lance and go deep frost/arcane. Opens up a ton of different ways to play if that’s the case. I honestly think it would solve a ton of issues.