I interpret these tweets to be more of a warning to Wikileaks' enemies rather than being directed at the general public.
When - February 22nd - the engine is from an F22 raptor, so i think they are hinting they will release something big on Feb 22nd. Also note that the pic was taken in Langley Virginia which is CIA headquarters, more on that below.
Who - the source of the leak is someone similar to Manning and Snowden, perhaps an ex-CIA spy, as other pics had a relation to Langley.
What - i think the seed-bank is indicating that the source of these new leaks is protected from harm in the same way as the seeds in the seed bank. Either the source or the actual data itself, again my interpretation is that these are warnings to insiders who want to prevent WL from leaking.
Just my interpretation.