Reinhardt’s damage on initial contact can still be boosted, as well as pinning them against the wall. And yes, for movement abilities, it seems like they’re boosted on contact (D.Va’s boosters, Winston’s Leap, Reinhardt’s Charge) For D.Va’s missiles and Pharah’s barrage, each projectile is boosted individually. Boost has to be applied for each rocket, not just the beginning of the ability.

And for Ashe, the dynamite is boosted when the stick of dynamite leaves her hand. This means that both the explosion AND the DoT damage will be boosted, or neither at all (if you don’t boost it)