I think DavidH's option 1 would be most useful. While the leap can handle persistent tracking of fingers, when the hand goes perpendicular to the sensor, the accuracy diminishes. Being able to add an orthogonal perspective would help alleviate that, and maintain accuracy for more hand positions - really useful in research settings.
It seems now that that is almost possible with the beta's device enumeration (and adding in a check of the inactive device's confidence if the active's confidence drops below some threshold) but maintaining the position in the render is near impossible.
Support to identify Hand IDs relative to other devices would be key. That is, at the device transistion, apply a relative transform of the data to maintain 3D coordinates.