Unless…unless, of course, she meant that the show would hold onto its bigger secrets even beyond its final episode, keeping the mystery alive until…
Arrow tends to use the 18th episodes from each season to flip things on their head with twists and big moments, so that might be when one is revealed.
And if we’re taking some vague mathematical assumptions here, Wendy Mericle’s ominous uses of “some will happen” and “much later” implies we may have to actually wait until the Season 5 finale to get some real answers.