User blog comment:Menara/The Son of Sobek: The official PJ and Kane Chronicles Crossover/@comment-122.164.234.74-20130210100534/@comment-3146930-20130210140906

He never stated he would never do a crossover. If you check his website, one of the frequently asked questions is would he do a crossover to which he said:

"I don't know. Yes, the worlds exist side-by-side. You've probably noticed some 'shout-outs' to the Percy Jackson series within the Kane Chronicles. I think it would be pretty confusing to mash the two series together, though! It's tough enough keeping one set of gods straight. Two might be hard. If I ever wrote a book like that, it would be quite some time from now. Remember, each book takes one year to write, and I've got a lot of other books to write first."