Didn't he also say that they'd never kiss? And that Eternity Code was the last book? And meanwhile, in the books, which is what actually counts as canon, Artemis has developed an alter dedicated to pursuing Holly, who claims that Artemis thinks about her all the time, and has "all of his passion," while Holly worries about him, wants to hold him, still thinks about snogging him, and is willing to risk her life for him. I'm going to stop thinking they have potential as a couple when Colfer stops writing it.
And the "completely different stages in their development" thing doesn't work. What about Arwen and Aragorn, referenced by Artemis himself? What about Doctor/Companion? (I am finding an excuse to work the "You can spend your whole life with me. I can't spend my whole life with you," quote into a fic. Somewhere, it will be put.) What about all the many, many human/elf romances that have existed over the years? If you want to argue physics of the relationship, that's another matter, that I can't have a PG discussion about, but I have some ideas as to how it can be circumvented.