Why on earth do people think this is to the detriment of publishers? This will effectively just lock in their profits by forcing all eu grants to include the cost of payments to publishers to make research papers open access. It just means the taxpayer is now paying for open access instead of individuals having to pay up themselves. Note I'm not saying this is a bad thing, and it is possibly worth publicly subsidisin…
It does however provide a limit on how much money each publisher can extract from a paper, and makes things far more transparent. It also makes free or cheaper services more competitive.
I'm not sure if there are any more details available yet, but I would worry about this turning into even more of a gravy train for publishers. I can't see for example the Dutch government being in any hurry to introduce any legislation that will threaten Elsevier's viability.
Nonetheless it is still a positive step that scientific findings look like becoming more readily accessible for the general public.