I know that Watanuki made the wish to see Yuuko again, but I thought that the payment for this wish was his removal from time - meaning, his inability to age while those around him do. For instance, he still looks as he did as a teen, while Doumeki and Kohane both have grown. My understanding was that Watanuki's inability to leave the shop was payment for another wish - one he and Syaoran/Tsubasa paid together, to escape Fay Wang Reed's trap. Syaoran/Tsubasa can never stay in one place permanently, meaning he is kept from living with Sakura/Tsubasa, while Watanuki can never leave the shop. Am I wrong? I thought this was the case after having read TRC, but the discussion threads all seem to support the idea that Watanuki can't leave the shop because of his wish to see Yuuko again, so I'm a little confused.
If my conjecture is correct and Watanuki must always stay as Syaoran/Tsubasa must always go, then, possibly, they could in the future switch places as they are paired, or two halves of a set, like the black and white Mokonas. The black Mokona has said before that he misses the white Mokona because of their connection, and that when objects or favours pass between the two of them there is no payment needed as they are the same; maybe the same could happen for Watanuki and Syaoran, and they could both have happy (happier?) endings. Of course, the fact that Syaoran did pay Watanuki to travel through dimensions makes this theory less likely, but maybe Watanuki doesn't realize what their connection entails? Like, all the possibilities in its use?
I don't know, I just wanted to get my first question cleared up and then maybe offer an idea for exploration.