We recently cruised on QV in December for 12 nights and found no issues with open dining.
We dined both early 6pm, 7pm and once at 8pm and there was never a problem getting a table for 2. There was a small queue a couple of nights but it all seemed to work well.
We did miss the familiarity of having the same wait staff each night though.
It was interesting to sit in different places on Deck 2 though. A couple of evening we were right at the aft and the view was wonderful.