We're thinking on adding the following methods:

/// Indicates if the specified element defines a collection of behaviors
static bool HasBehaviors(const DependencyObject* obj, BehaviorCollection*& behaviors);

/// Indicates if the specified element defines a collection of triggers
static bool HasTriggers(const DependencyObject* obj, TriggerBaseCollection*& triggers);

Would that solve your scenario?

Yes it would!

Or to clarify, would the second parameter here be optional? Or if not, would it simply set the pointer I pass in to nullptr if there is no collection?

The idea of the second parameter is just a minor optimization to get the collection if it is already set:

BehaviorCollection* behaviors = nullptr;
if (Interaction::HasBehaviors(obj, behaviors))
{
    // do something with 'behaviors' collection
}

We can also offer a simple HasBehaviors(obj) and then you can call GetBehaviors(objt) to get the collection, it won't make much difference.

Ok sounds good! I'm not picky about the actual interface here, I just want to make sure that if the element doesn't have behaviors, then I have an option to not mutate its state