I grew up in a house with a basic aluminium kettle designed to be used on an externally heated hob. http://www.dreamstime.com/stock-photo-very-old-kettle-isolated-image16622230
Although we did not possess one ourselves the height of kettle technology at the time was a similar externally heated vessel with a whistle attached to the spot which made an audible noise when the water was boiling vigorously.http://www.ecvv.com/product/459875.html
I was still quite young when we purchased our first electric kettle. This object of wonder was made of stainless steel rather than aluminium but it had a similar shape to the kettle it replaced. An internal electric heating element meant water could be boiled without the aid of a stove. It also boiled its load of water a good deal more quickly probably because the heating element is fully immersed in the water. http://www.ebay.co.uk/itm/VINTAGE-RETRO-RUSSELL-HOBBS-ELECTRIC-KETTLE-/291114219730?pt=UK_Homes_Garden_Kitchen_Kettles&hash=item43c7c278d2
(Note: I should point out that electric kettles had been around since the early 20th century but they did not become commonplace in Ireland until the 1970's).
The whistling spout innovation did not survive the transition to electric kettles because a much more ground breaking development made it obsolete. Although the first electric kettles were dumb heating devices later models included a thermal switch above the level of the water which switched off the kettle once it was boiling sufficiently to generate a lot of steam. This truly was a wonderful innovation as it freed you from the need for constant vigilance while the kettle was plugged in.
The next significant innovation was the plastic jug kettle. I can still remember general scepticism that a plastic container could withstand the heat of boiling. Nevertheless they worked and soon became quite dominant in the market. The characteristic jug shape of plastic kettles required filling through the spout.
A minor innovation that plastic kettles allowed was the inclusion of a transparent panel allowing you to easily see the water level.
The next significant innovation was the powered base and detachable kettle. Early examples used a rigid joint so the kettle could only be put back in one position but it was nevertheless a significant advance in convenience and safety allowing the kettle to be removed from the base for filing and pouring without the incuberance of a trailing lead. http://www.ebay.co.uk/itm/1-LITRE-WHITE-ELECTRIC-CORDLESS-TRAVEL-KETTLE-SMALL-JUG-SUITABLE-FOR-HOLIDAYS-/350722664826 (Picture is a travel kettle but the original plastic kettles looked just like this).
A minor enhancement was the replacement of the rigid base with swivelling base. This allowed the kettle to be placed on the base from any direction.
Also around this time the traditional immersed heating element was replaced with a flat heated baseplate. The older heating elements required a substantial minimum volume of water to cover the element but the flat heating plate could be safe with as little as one cup of water.
Stainless steel came back in a big way with the development of the composite steel / plastic kettles. These combine the attractive robust finish of stainless steel with the features of the plastic jug kettle specifically the detachable base and the water level window. There have always been variations in aesthetic design and various metal, plastic, glass and ceramic finishes have been used for kettles over the years but the composite stainless steel / plastic jug kettle remains very popular to this day. http://www.jarrold.co.uk/departments/house-and-home/kitchen/kitchen-electrical/russell-hobbs-compact-kettle
That pretty much brings us to the present day. During a recent kettle shopping expedition I was somewhat disappointed to note that internet connected "smart kettles" are not yet a reality but temperature control is the new must have feature with various settings from a lukewarm 40° all the way up to boiling 100°C.http://www.amazon.co.uk/Cuisinart-CPK17U-Kettle-Brushed-Stainless/dp/B003UFQTYI/ref=sr_1_4?s=kitchen&ie=UTF8&qid=1396890377&sr=1-4&keywords=temperature+control+kettles
Please note that this article relies on no greater scholarship than my own hazy memory so I claim no authority on the subject and none of the images are my own. Copyrights belong to the respective authors