Green Energy

It's not the range. With this technology, it's just the combination of fuel and exhaust that makes it unlikely to reach peaceful applications sooner.

A user of this technology must be willing to tolerate (and cause) considerable inconvenience just to increase the range of their electric aircraft.

Fuel distribution would be an annoying but surmountable problem. Not the easiest, but doable. Sodium needs to be stored either in mineral oil or inert gas. Otherwise it will spontaneously oxidize quite fast. Airports would need sodium warehouses with specialized equipment (either oil baths to submerge it or some kind of lockers with an unbreathable atmosphere). Trucks with the same kind of equipment would be needed to deliver the stuff. Maybe a bottle system could be devised, whereupon sodium is solid in a bottle and the bottle is heated above 100 C to pour it out.

Fuel production efficiency would be a problem. I don't know the efficiency of sodium production, but intuitively this is likely to be around 80% (plus road transport). Charging a battery from the grid is more efficient, so the user of this technology must either have cheap electrical energy (this might be true in future with lots of renewables) or be willing to ignore the cost of energy (military users will do that already now, just promise them a bit more flight range).

Finally, public debate about a caustic exhaust stream is likely to be non-trivial. I predict that people will be quite worried about the direct effects of NaO and NaOH air pollution - it's one of those things which is clearly health negative, even if climate positive. Convincing people that it's safe will require studies about how quickly NaO turns into NaOH, and how quickly the exhaust stream neutralizes and becomes safe. Unsurprisingly, military users are pretty unconcerned about being health negative - most of their tools are like that.