The biggest impediment (and it is insurmountable) to a Jin Yong/Gu Long wuxia universe crossover is that Gu Long has been dead for over thirty years. In terms of the mythos and continuity of both universes, however, if they were to do a DC/Marvel style team up (like in the comics; it's probably never going to happen in the movies), are there any real impediments? I feel that Gu Long's predominantly Ming Dynasty-based stories (e.g. LUK SIU FUNG, DAGGER LEE, CHOR LAU HEUNG, etc.) can coexist with Jin Yong's canon. For example, the Ngor Mei Sect was founded by Gwok Seung in the Jin Yong universe, but nothing (other than copyright) really precludes her from also being its founder in the Gu Long universe. We already had Luk Siu Fung encounter the Cheun Jen Sect's 7 Stars Big Dipper Formation in the third novel of his series (BEFORE AND AFTER THE DUEL), and we all know of the Cheun Jen Sect's prominent role in Jin Yong's CONDOR HEROES TRILOGY.
It's an interesting thought exercise, at least. Imagine LSF comparing his Ling Sai Finger Technique to the Deun Family's 1 Yeung Finger Technique.