How much do you want to bet that the people proposing this are worth at least one or two orders of magnitude more than EUR 500,000. To quote from the article "The group say they have more money than they need", and very few people with a net worth of just above eur 500,000 fall into that category.
44 people have signed a partition to propose a tax law that will negatively affect 2.2 million people, am I the only person who sees something very odd with that. This is nothing but a bullshit PR move by some rich heirs to try to buy some good will.
And EUR 500,000 is hardly a "fortune" - that's about GBP 400,000 which is the price of an ordinary family home in the South-East of England, or the price of a two-bedroom flat in central London. So effectively, this is an upper-class heir to a family fortune advocating higher taxation on the middle-classes and professionals.