It's an interesting question. Switzerland is thinking of abandoning people in favor of abstract designs. The advantage of not using faces is that it makes it easier to circulate the banknote outside of the country.
==========
The question of what is the purpose of banknotes is becoming an issue for wealthy nations. The British have a very practical view of banknotes based on the counterfeiting scare in WW2. Prisoners in concentration camps were so effective in counterfeiting the British pound that all the currency above £5 was withdrawn from circulation. Even today, there are only three £50 banknotes per person circulating in the UK. Most transaction are done with the £20 banknote. So they are for routine small purchases (mostly legal). Most people don't hide large amounts of money.
==========
Britain is becoming somewhat unique now in the world. USA circulates over twenty $100 banknotes per capita. Most of these banknotes circulate overseas making a huge profit for the US treasury. The era of printing thousands of dumptrucks full of $100 banknotes primarily began in 1991 when the Soviet Union fell.
==========
Similarly there are almost three 500 Euro banknotes circulating per person. These huge banknotes are fueling illegal drug transactions, money laundering schemes, and all kinds of weapon sales. Once again making a huge profit for the central bank.
============
Switzerland is also circulating many banknotes.They circulate more than three 1000 franc notes (worth £600 or $1000 apiece) per citizen. By removing the national symbols, they will probably start circulating in Africa and Russia where they will make a profit for the central bank.
============
Japanese are the largest users of banknotes in the world. Although they do not have a banknote with a high value (10,000 Yen is worth around £70) they print a huge number of them. People use a lot of currency. I don't know how much circulates oversees.
============
As the oldest central bank, the Bank of London seems like it is not interested in trying to compete in this rush to capitilize on currency. I think that if the Bank of England announced that they would only be printing £5 £10 £20 banknotes, and eventually the £50 note would be phased out, the majority of people wouldn't even care.
============
There are two other wealthy nations without high value banknotes, South Korea (perpetually afraid of counterfeit operations) and Iceland. Iceland is relatively unique in Europe in that it's highest value banknote is the 5000 krónur (£25 pounds). So if you are trying to conduct a large scale illegal cash operation in Iceland, you need a suitcase full of cash.