But eggs still come in dozens, and bottles in boxes and a host of other items, even in metric countries. Then there are months in the year. So the 12 times table is universally useful still.
On history, Gove is re-introducing the 1950s syllabus, prehistory to Saxons in primary school, Normans onwards in secondary. If you opted for science O levels you never got past the Stuarts, if you only did O level it stopped in 1815 and you only got to relatively recent times if you did A level history. Personally I think the concept of prehistory and the imagination required to understand the concept of life 5 - 10,000 years ago is very difficult for 5 - 7 year olds.
DGC (aged 3 & 6) adore the Horrible Histories and have grasped a real sense of the chronology of history since the Normans with that. DGD comes home from school and looks online for more information on Florence Nightingale and Grace Darling and uses her grasp of the sweep of British History gained from the HH's to understand when they lived.
I find knowing to within 5 years when a monarch was reigning is very useful in pinning down many aspects of the past. When we bought our current home we were told it was late 16th century, I could place this as late Tudor as I knew Queen Elizabeth died in the early years of the 17th century. It gave me a context for the house. When later scientific dating discovered it was built in 1467 I knew it dated to the War of the Roses and Edward IV and I adjusted the context of our house accordingly. The same thing applies when visiting any historic site, whether a house, castle or any other historic site.