OK...that is exactly my point. Not all aircraft are certificated factory built. The J3 & J5 predecessor to your SC had no electrical. Still lots of them flying that way. 7AC, Luscombes, etc have no electrical. So they don't have to have the ads-b so says the Feds. What would power it satisfactorily?

Home builts can use non-tso'd ads-b boxes. Much-much cheaper, but still too big to mount under a Phantom pro. I don't have any real prices at hand, I think it's too new.

So, if one stays in uncontrolled airspace, no need for ads-b. If drone is flying in uncontrolled airspace, why is there a need? ads-b is not needed for G airspace (uncontrolled), just like flying your SC thousands of miles w/no xpdr. If the rule is made that ads-b is NOT required for any aircraft in G space, then we keep that Phantom 4 & J5 in G airspace. 

If any of the aircraft or drones are not going to operate in the exempted airspace (G at this time), then they don't need the equipment, regardless of how much either are hated.

Finally, drones are now being equipped with Lidar to make localized mapping much easier & quicker.