I'll try to answer - JMHOs:
Have we had a final action go against us? No (584?)
If not, are they possibly warning of something coming? Not necessarily (see below)
Or, were they implying that a Final Approval of the patents isn't final because there may be someone else waiting in the wings to challenge it again? Yes. There will always be a chance, however remote, that someone/infinger, will again challenge the patent claims. The key is that as time passes, and as the patents are refined via amendment, and as we see continued success at the PTO, the probability gets more and more remote.
SGE