This will be of little use for the Ukrainians. If they (legally) can't work in the European Union, then what is the use in having a visa free regime? I assume that a lot of them will start working illegally. Some will apply for the refugee status as well, especially those from the Donbass.
And what prevents to do that now? Visa-free regime need more Europe than the Ukrainians. Those who want to illegally work in Europe for a long time and no working visa this is not a hindrance.