They won't do Kurofai. They said it directly at AX2006 CLAMP panel.
They laughed at it though. Who knows? Maybe they took it into consideration so that's why they made the Kamui/Kurogane Blood thing. Don't forget that they're women too, so they know exactly what fangirls want. As for boys...well they caught my attention, lol. Yukito and Touya was pretty surprising, I can't exactly say they're gay though, even though they did say they love each other lol. CCS world was pretty messed though, they really showed that love can be expressed in every way. Fujitaka with his late wife, Nadeshiko, Touya with Yukito, Eriol with Mizuki, Terada (some 20+ year old teacher) with Rika (10 year old girl), Yamazaki with Chiharu, and finally the most important, Syaoran and Sakura. Oh, don't forget Meilin who's in love with her own cousin!
Anyways, as they see it they're only strong companions(Kurogane and Fai). They wanted 2 adults to guide Syaoran since he's still only a kid. One who's great at fighting, one who's great at dealing with emotions with smiles, and the one inbetween (Syaoran). They certainly share a strong bond of friendship, but sorry girls, nothing more. Put it this way though, seeing the situation that he'll only accept Kurogane's blood, means that they'll be together in the end somehow. Not as lovers though, but maybe in some magical way that CLAMP always makes it. They might even die for Syaoran and Sakura's sake. Heh, we'll just have to wait won't we?