There should be an announcement on the tannoy that fans entering the field of play at any time before, during or after the match will receive a lifetime ban from Goodison and the new stadium. The announcement can be made several times in the hour before kick off, plus at half time, and also put on the big screen.
That said, what are the FA gonna do? City just had about 10,000 fans on the field last week and there's been nothing whatsoever said about it in the media. Seems like it's only reserved for the so-called smaller teams.