* feasibility of this new technology is due to the commoditization of three necessary components over the last few years: cameras (improved immensely in both quality and cost due to the smartphone revolution), drones/UAVs/small satellites themselves, and services like AWS that allow small enterprises to crunch huge amounts of geospatial data at little cost.
* there's good reason to believe that the commoditization of those components (i.e. availability and quality) will increase in the next few years.
* drones of the popular quadcopter type are a mixed bag -- their range is very limited because the batteries required to operate them are very heavy. This is tough because they have to survey huge areas. For large areas, many drones are required, which poses a significant overhead cost. However, what's nice about them is that they can be used with surgical precision: if something looks weird, drones can fly very close to the ground and take high-res pictures.
* conversely, what's nice about UAVs and small sats is that they can capture geospatial data on huge areas much more easily (though in lower resolution).
I think we're generally going to see a kind of two-tier approach, in which a high-altitude machine (a UAV mini-plane, or even higher up, a small satellite) does the broad aerial surveillance, and a low-altitude machine, i.e. a quadcopter drone, is sent out for random sampling to cross-reference the geospatial data, and for surgical investigation of abnormalities. The economic benefits of such a scheme could be quite significant for farmers.
I'm also looking forward to drones with more sophisticated sensors -- for example, heat or IR cameras. These are pretty rare on the market so far. Regrettably, they aren't being commoditized in the way that regular cameras are, so progress on this front may be a little slower.