Is this due to lack of confidence in the code base, some known issues like incorrect conversions or for some other reason. The extension is around for some time now so ...
Topic on Extension talk:CoordinateConversion
This is my first MediaWiki extension and one of my first PHP-projects and it is only tested on one site. In particular, it has not yet been sufficiently tested under various conditions. As far as I can tell, it doesn't give really incorrect results, but I am a bit uncertain about the accuracy; +/- 1 m, +/- 10 m, +/- 100 m? Especially because I do not know the accuracy of calculations in PHP.
Still planned functionalities are SMW / Maps compatibility and heights. It already depends a bit on Maps/SMW because it uses a library installed by those extensions. The planned / target error is 1 to 10 m.
This question was indeed just to get insight into the status of the extension. I believe other interested parties will appreciate your information here, too.
It is a really good effort. Since I am not a programmer I value a lot that you dare working on this.
Then it comes to accuracy I will once I installed the extension contact someone who will be able to assess at least for the Swiss conversions created.