I’d like to understand what exactly the criterion is for whether an attack of this nature is possible.
My gut feeling is that really anything where the 4x upwards difficulty adjustment limit is triggered is exploitable in a way. If so, any solution will involve directly or indirectly requiring that the last timestamp within a window is at least 3.5 days (1/4 of 2 weeks) after the first timestamp (effectively outlawing the 4x limit from having an effect).