There is over a week left in August, the whole of September, October and even possibly November. Who knows whether the season ends late September or very much later?
Two ways of looking at it. Admit defeat now and leave it in the nuc or be positive and go for a full (or almost full) brood box.
They can always be put back in a nuc if they do not fare too well in the full box. The full box can be reduced with insulated dividers, if a couple frames short.
You have enough colonies to reinforce this one, depending on their state of course. You could use excess brood from the nuc to help other colonies, if you decide to start winter shut-down preparations now.
You could get a second storey for the nuc. Nucs often need extra feeding in the winter. Mine don't, but they would normally be 6 frames of 14 x12 and likely a shallow box above in a poly-box. You choose your plan and go with it.
Down to you, but just some things to consider.
RAB