Wuxia stories are typically set in pre-modern (by Western reckoning) times...generally the centuries corresponding to the European Middle Ages. The two stories set latest in the Jin Yong universe were BOOK & SWORD: GRATITUDE & REVENGE and the FLYING FOX OF SNOWY MOUNTAIN stories, which unfold almost concurrently during the reign of the Chien Lung Emperor (mid-18th Century).
In the West, the mid-18th Century was the time during which the Scientific, Industrial, and Political Revolutions were about to begin. By the end of the century, the United States of America would come into existence, and so would early railroads and factories. Clearly, the times were a changing.
The modern world is not one that comfortably accommodates wuxia stories. It's not that martial arts ceased to exist; it's that the kind of society that underlay wulin went by the wayside as China modernized. With that in mind, would you agree that the mid-18th Century era during which the BOOK & SWORD and THE FLYING FOX stories were set was as late as credibly acceptable to sustain a wuxia story in the Jin Yong wuxia universe, or could Jin Yong have possibly squeezed out a wuxia story set as late as the 19th Century (or even very early 20th Century) without the whole exercise seeming ridiculous?