I doubt there will be a true Hardyesque "Mr. Worf, fire!" cliffhanger. AFAIK, the only film to ever do anything close to that was the second Matrix
film. However, I've been saying all along that I fully suspect STiD will end on a "soft" (for lack of a better term) cliff along the lines of ESB or TDK.
STiD's plot will be fully contained, but there will be unresolved plot feelers that set-up ST3.