To me, it makes absolutely NO sense for them to reprint the ally color brood leaders in DTK. Just because DTK is ally color themed, does not mean they will do so. It makes more sense for them to print enemy color legendaries, than reprint (even with new mechanics) dragons they printed last set. The khans in different roles, those make sense since they will be ally-colored(maybe) and would have changed simply due to that fact. (The old khans might be enemy colored since, as an example, the dragon bell was known to be white themed in FRF. (Zurgo may be RW or BW in DTK.)
Edit: I think Narset will be a UW or UR planeswalker. She will be the only 'Khan' that isn't reworked in the new set.
Edit: I think Narset will be a UW or UR planeswalker. She will be the only 'Khan' that isn't reworked in the new set.