We are just hitting the tip of the iceberg with Part 107. While Part 107 is far less restrictive than a 333 waiver or even under the model aircraft rules, it still is far too restrictive for the technology that exists today. The FAA knows that flight BVLOS, night flight, flight over people, UAS more than 55 pounds, etc. are all quite possible to do safely with the technology and that in the not too distant future they will need to address these issues. Still if we limit our vision to these issues we are not being very imaginative.
Flights to deliver Pizza, packages, even people using UAS is all quite possible to do safely with the technology that we have today.
If we stay below 400' there is a lot we can do, and will do, even in this limited airspace.
While other manned aircraft are a concern, particularly helicopters which are allowed to go lower than 500' (see C.F.R. 14 Part 91.119), they are not the problem.
The real problem is other UAS operating below 400'. How are autonomous drones to avoid each other? Drones must be able to sense other drones in real time with enough time for them to avoid each other. Short term this is probably ADS-B, long term I am not sure that ADS-B will hold up with the number of drones we can expect to see. We probably will need something that is more limited in range and is more drone to drone than ADS-B.
The other item we need is far more low level detail for the terrain the drones are flying over. Enough detail that they can safely fly at very low altitudes autonomously without hitting stationary objects. I can easily envision a future where a building permit must include data base update for drones.
The remaining issues are non-stationary objects such as sailboat, building cranes, even ladders. Perhaps someday the tables will turn and someone wanting to use a ladder that is taller than 10' will need to issue an electronic NOTAM.
Technology has a way of catching up with sci-fi. The first iPad I saw was on star trek, the first apple watch I saw was on **** Tracy, and I believe some day I will be able to say the first drone I saw was on the Jetsons. (Note the ADS-B antennas on the bottom)