Well, I'd rather see a DouWata pairing than anything else, but it's possible Watanuki might end the series not being paired off with anyone. It has to be someone who's significant in his mind, and right now that's really just Doumeki, Himawari and Yuuko. Like you said, Zashiki Warashi isn't central enough..and even if there end up being no pairings at all, I'll still love this manga. It's one of the most brilliant things I've ever read.