Looking at the statistics makes me wonder if you were the only one who ever downloaded the source code
Seriously. The reason to move the project to SourceForge was that discussions about the C source would be rather off topic at DosTips. But apparently nobody really cares about the source code. The majority of people just downloads the binaries and leaves the source alone. Thus, I don't get much feedback about the source over there (as I don't get much feedback at all). GitHub is nice for developing in a team but according to the little interest in the source I don't expect any contributors. I like built-in features like the Wiki in the SourceForge projects. I'm not familiar with web development and I'm neither able nor am I willing to write a buch of html only for some further explanation of the tool.
tl;dr SourceForge was a good choice for sharing CONVERTCP imho.
Basically I agree with you about the support of XP. But this project has its history. It was explicitly developed to work on XP. Saso is the father of CONVERTCP, once he asked me to write it and he still works on XP. Also if you have a look at the recent feedback I got - one asked for supporting a vintage charset and one complained about the broken option on XP. So, as long as the tool keeps being compliant with the most recent Windows versions I'll still consider to update it accordingly.
You're right about the dependencies. But that's nothing I want to change. I could have used libraries like ICU but I'm afraid that would destroy the performance and just bloat the tool. Beginning with v7 you have at least the possibility to incorporate custom single-byte charsets. When I thought about the format of the charmap file I already considered the possibility to extend it to multi-byte charsets if there was any feature request in future.