The IMC rating was a UK only rating dating back to before the UK joined EASA. It was very effective in reducing fatalities caused by the unpredictable British weather. It was intended to get private pilots safely on the ground when trapped by weather.
EASA wanted to scrap it in the name of unification but after much argument with member states all having different agendas they came up with the idea of the Basic Instument Rating.
As usual they gold plated a simple idea and added more training hoops to jump through to qualify. When fully implemented the derogation which allowed the UK to retain the IMC rating will end and the same rating will apply throughout EASA.