agree- that is great looking brood! Is that the hive that you suspect is queenless? If so go ahead and get a frame with fresh eggs and small larvae on it from one of your other hives and swap it with a frame from that hive. Place it near the middle somewhere where the bees cluster. Mark it at the top so you know which frame it is. If the bees are truly queenless- they will soon start making another one. with all that capped brood the population of that hive should soon recover. You could check that frame again in 4 days or so to confirm that the bees have made a start to at least one queen cell- and/or to recheck to see if there are any eggs visible anywhere- in case maybe you have a queen after all.
When checking take care as a queen cell might be protruding and could get dmaged. After the four days- assuming there is a cell- leave the hive along for around 1 month- by that time the queen should be mated and laying. Apparently the new queen is very vulnerable aroudn the time she emerges and over the next week as she dries out and heads out for mating flights. It’s best to leave the hive well alone during that period.
I just re-read what you wrote and saw that was already your plan.