The rotation of 2 Arcane Blast and Arcane Barrage is currently recommended for single target. However, this rotation changes in multi-target situations and in most pvp situations.
In a high movement situation, for example, an arcane Spellslinger would still be able to make his heroic tree work by casting Arcane Missiles and 2 Arcane Barrage, which will no longer be possible.
Unless Blizzard greatly increases the damage of our abilities and leaves the damage of the hero trees practically negligible, there is no decent scenario in which we wouldn’t want the main features of our hero trees to trigger.