IMO, the characters of Mr K and JF would be quite well-suited to each other -- but perhaps they are a lttle too like each other in their serious dispositions? In P&P Eliz's liveliness and Darcy's seriousness complement each other, in Persuasion Anne's and Frederick's characters also complement each other, although in MP, Fanny and Edmund are rather alike -- but Edmund had at first wanted the lively Mary Crawford and rejected her only after he found she had "faults of principles", and he had also thought that Henry's lively disposition could complement Fanny's seriousness, and that she would be a good influence on him.

So -- could Mr K and JF make a good couple, or would they be too serious and rather boring if they were together.