When I read the manga I'm thinking of the point of view of the character and it seems that Heiji is in love with Kazuha. I wrote a big reflexion about this point on my web site.
But I'm fan for 10 years. And I don't think about DC only from the point of view of a fan. I also have acquiantances who are working in animation studio in France and in Japan or who are comics drawers, and I know the world of mangaka and the world of the animation studio is not so fantastic as people (especially manga fans) imagine it. I translated in french some interview of Gosho's working life (one part is in the Conan Drill) and I realized how hard is his job. I also know Gosho doesn't decide everything by himself. The DC publisher decide a lot of points in DC universe. Did you know for example that Heiji's appearance in volume 10 was not the original idea of Gosho? He originaly planed to draw the first appearance of Haibara. The publisher decided that he should create a new character (a friend rival) in this volume and Heiji was created.
So knowing all this informations, my point of view is a bit different from an usual fan. That doesn't mean I'm true or something. But just I don't think about DC in the same way as you may do it.
So now that's true, I'm thinking about the Boys Love point of view. I'm sure the publisher doesn't plan to make it official or something but they consider the popularity of the BL for the readers. And they give them some fan service scenes. Doing that, the fans who love canons are happy because BL or CoxAi or what you want will never be official, and the fans of non-canon are happy because there are still fan service scenes for all of them.
I'm pretty sure the only reason Gosho accepted to draw Kid in DC was for the fan service (and because the editor asked for it). Kid doesn't have any other role than the rival and without girlfriend (in DC), he is the perfect candidate to be the BL lovers of Shinichi. In Japan, in the FANS WORLD (that's not true for normal readers) the most popular couple is ShinichixKaito. ShinxRan is the third couple, just next to HeijixShinichi. (I made an analysis in my website. I don't think you need to speak french to understand the graphics results. If you are interested, you can ask me)
Sorry, this answer is a bit off topic. But that explains why I consider the interest of the publisher when I think about the possibility of the developpement of the main plot or the romance plot.