Okay, I'll try to be more clear. CLAMP enjoy creating cute moments between characters who aren't their canon couple. Those cute moments generally go nowhere since CLAMP make sure their canon pairing will remain the one they had estabilished from beginning and rarely a character have a feeling for a person and then move to another (an exception is 'Card Captor Sakura' where both Sakura and Syaoran believe they have feelings for Yukito and then then fell for each other).
'X' is still unfinished so we don't know what will happen to Subaru or Fuma.
Maybe they'll both die. Maybe one of them will die. Maybe they'll both move over (even if I doubt it).
However we're talking about possibility here. While CLAMP generally NEVER break a canon pairing if you're writing a fic, for example one placed in the end of 'X' you can use those cute moments to create a background that will allow the characters to still be IC and be together. In real life it happens that friendship will move to something deeper. The fact that Kamui and Subaru are close as 'sisters' as CLAMP pointed out in an interview could develop with time in a deeper feelings. So while I'm sure there's nothing more than a 'sisterly' relation between Subaru and Kamui in 'X' and, knowing CLAMP, I expect them to keep this as such developing the plot of 'X' and 'Tsubasa', I would say it's still possible for another person write a post-'X' or a 'Tsubasa' fic that will be in character and write a Subaru/Kamui, even if I personally hate this pairing.
As for believing if CLAMP would hint something... yes, I definitely believe they would. CLAMP has an amazing commercial sense and would give to the fans chances to develop the story in their mind the way they prefer as long as they keep reading it and buying gadgets. After all their work is to sell their manga.
While X main pairing is Fuma/Kamui, there are hints for a Kamui/Kotori pairing that satisfy etero couples fans and Subaru/Kamui to satisf yaoi fans that want a nicer relation and even Keiichi/Kamui hints that satisfy fans that want a less angst pairing. CLAMP will never get to all those overmentioned pairing a chance (Kotori died, Subaru seems too caught up in his grief, Keiichi... no idea) but this doesn't make them impossible if the writer place them in the right setting. And no, this won't make them OOC just because they get different chances. The character would stay the same.
If you ask me which one is the canon pairing I'll say FuKa and SeiSu. If you ask me if the pairing Fubaru is impossible I'll answer I don't believe CLAMP will ever develop it but that this doesn't make it impossible. It's just a plot choice.
What I mean with 'hinted' isn't that there's love between to chara but that there's a chance for them to develop a relation. So there are hints in 'X' for Subaru and Kamui. It doesn't make them in love as CLAMP stated. It only gives to this feeling the chance (that I don't think CLAMP will ever use) to develop IN THE FUTURE into a relation. It posts the basis for a possible FUTURE relation. It doesn't estabilish there's one. The fact that CLAMP decide/will decide to not develop this chance doesn't make it rationally impossible.
Part 1
CLAMP enjoy creating cute moments between characters who aren't their canon couple. Those cute moments generally go nowhere since CLAMP make sure their canon pairing will remain the one they had estabilished from beginning and rarely a character have a feeling for a person and then move to another (an exception is 'Card Captor Sakura' where both Sakura and Syaoran believe they have feelings for Yukito and then then fell for each other).
'X' is still unfinished so we don't know what will happen to Subaru or Fuma.
Maybe they'll both die. Maybe one of them will die. Maybe they'll both move over (even if I doubt it).
However we're talking about possibility here. While CLAMP generally NEVER break a canon pairing if you're writing a fic, for example one placed in the end of 'X' you can use those cute moments to create a background that will allow the characters to still be IC and be together.
In real life it happens that friendship will move to something deeper. The fact that Kamui and Subaru are close as 'sisters' as CLAMP pointed out in an interview could develop with time in a deeper feelings.
So while I'm sure there's nothing more than a 'sisterly' relation between Subaru and Kamui in 'X' and, knowing CLAMP, I expect them to keep this as such developing the plot of 'X' and 'Tsubasa', I would say it's still possible for another person write a post-'X' or a 'Tsubasa' fic that will be in character and write a Subaru/Kamui, even if I personally hate this pairing.
As for believing if CLAMP would hint something... yes, I definitely believe they would.
CLAMP has an amazing commercial sense and would give to the fans chances to develop the story in their mind the way they prefer as long as they keep reading it and buying gadgets. After all their work is to sell their manga.
While X main pairing is Fuma/Kamui, there are hints for a Kamui/Kotori pairing that satisfy etero couples fans and Subaru/Kamui to satisf yaoi fans that want a nicer relation and even Keiichi/Kamui hints that satisfy fans that want a less angst pairing.
CLAMP will never get to all those overmentioned pairing a chance (Kotori died, Subaru seems too caught up in his grief, Keiichi... no idea) but this doesn't make them impossible if the writer place them in the right setting.
And no, this won't make them OOC just because they get different chances. The character would stay the same.
If you ask me which one is the canon pairing I'll say FuKa and SeiSu. If you ask me if the pairing Fubaru is impossible I'll answer I don't believe CLAMP will ever develop it but that this doesn't make it impossible. It's just a plot choice.
What I mean with 'hinted' isn't that there's love between to chara but that there's a chance for them to develop a relation.
So there are hints in 'X' for Subaru and Kamui. It doesn't make them in love as CLAMP stated. It only gives to this feeling the chance (that I don't think CLAMP will ever use) to develop IN THE FUTURE into a relation.
It posts the basis for a possible FUTURE relation. It doesn't estabilish there's one.
The fact that CLAMP decide/will decide to not develop this chance doesn't make it rationally impossible.