Overall surely it would be better for the majority of people if prices in London dropped a bit.
For people who do own property and want to sell:
The value will drop, but assuming they are selling to buy something else, anything they choose to buy instead will have dropped by a similar amount so it cancels out.
For people who do not own property and want to buy:
They can actually get on the property ladder
A few people who might be disadvantaged:
Baby boomers: Planning to downsize for retirement, they wouldn't have as big a nest egg from downsizing. However, assuming they have lived in the property for a while, the property is still likely to have significantly increased in value over the time they have lived there.
People selling to move out of London:
They wouldn't get as much as hoped for their property, so wouldn't be able to buy as big a property outside of London. However, assuming they have owned their property for more than 5 years, it has probably still gone up in value so much the drop would be small.