If you thought Amazon's recently announced plans to soon begin delivering packages by drone were the pipe dream of a company with more money than sense, the latest news might give you pause for thought.

In a long letter to shareholders published with the SEC, Amazon's founder and CEO Jeff Bezos said that the Prime Air team is "already flight testing our fifth and sixth generation aerial vehicles, and we are in the design phase on generations seven and eight."

Are these small tweaks or whole-scale redesigns? It's hard to tell from Bezos' laconic letter, but the revelations certainly show that Amazon Prime Air, as the programme is being called, is at least being taken seriously in the higher echelons of the e-commerce giant.

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A video released at the beginning of December last year showed packages being delivered by small quadrocopter-style drones, right into people's back gardens. While the video was widely derided as a hoax and a publicity stunt in the lead-up to Christmas, the latest comments by Bezos will hearten drone enthusiasts around the world.

Speaking on the 60 Minutes TV show over in the US, Bezos said that the quadcopters will be capable of delivering a 2.3 kg package to addresses within 10 miles of an Amazon fulfilment centre, within 30 minutes.

We can assume that many more generations will go through testing before this ambitious goal is reached. For now, the drones will have to contend with the not insignificant task of lugging a 2.3kg weight for 10 miles on a single battery.

The drone programme is expected to go live in the next 4-5 years.

Don't get too excited, though. While the letter mentioned drones almost in passing, most of it was dedicated to other flagship projects, like the Amazon Fire TV box, a direct competitor to Apple TV.

While 4-5 years might be a little optimistic, there's no doubt that we're moving towards a future that is increasingly ruled by autonomous robots and vehicles. There are absolutely massive gains to be made by speeding up and automating the retail experience, from warehouse to doorstep and every stage in between – gains that Amazon and other retail giants are guaranteed to take advantage of.