Or will they do what Paultons did and delay the opening of their big, expensive new investment until next season, when the Covid pandemic won't overshadow it? I don't know, I don't imagine they well but it wouldn't surprise me if they did tbh.
As said above, Paultons area was still incomplete, so it could be a while before it opens. There's no point opening a big new area for a couple of months of the season (I assume that at least part of the area won't be open during their winter period).
With Phantasialand, work is still ongoing, and they can still push it heavily during their winter event (and much like with Klugheim, continue to heavily push it into the next year).
It's much less of problem for Phantasia in both senses, so wouldn't really make sense in my opinion.