I read somewhere that this only applies to coins stored in custody wallets, is that correct? I am of the opinion that Germany is not a country that changes laws just like that, despite the fact that this particular law seems rather strange from the perspective of those in power, and incredibly good for every investor.

Croatia also has an identical model, with the difference that this period is 2 years, and that all crypto assets acquired before January 1, 2016 are tax-free. I think that such things will change only if a common agreement is reached at the level of the whole EU, which is completely unrealistic at the moment.