I never got the fanrage that the old D7/K't'inga in "Unexpected" caused. I actually really liked that they kept the classic design! The other designs of Klingon ships in ENT were nigh-on identical to the ones seen in the 23rd and 24th centuries anyway. The ship interiors looked exactly the same throughout Trek, with the exceptions of TOS (redressed Enterprise corridors) and STIII.
I say the planned D4 design looks virtually identical to the D7, except for holes in the nacelles and some (for lack of a better term) scaffolding along the wings. Not different enough to bother with.
See also my post here about visual continuity in Star Trek
, and how little I believe such visual minutae should matter. Similarly, the re-used Star Trek: Nemesis
uniforms on the Romulans or Ki Baratan city in season four doesn't matter, IMO.