Thanks for the info, @PW. Rumours to this effect were already doing the rounds.
I much regret this decision because some countries are highly likely to do increase MTOW for ultralights to 600 kg, Germany first of all, while others will staunchly refuse to. France comes to mind and, in their wake, Belgium too. The next step will then be that France no longer silently allows foreign ultralights.
No problem for Belgium, though: my silly authorities require an "overflight permit" for foreign registered ultralights anyway.
PS what does the ad referendum mean, in this context?