From my perspective, this is almost perfect for the development category. You are developing an OS project and writing about the updates. That's exactly what Utopian is for. The only changes I would suggest are to start creating a branch for each weekly update, then submit a PR highlighting the changes you made (not strictly necessary to make a PR per the rules but would help the moderator). You might have to shift your writing a little more towards release vs journal which is something only you can decide if you want to do, would vary on who the mod was though.

Personally, I feel like the blog post category is more aimed towards writing about larger mainstream OS projects. Reviews (but not tutorials), benchmarks, research or statistics. Just my take, it's a little difficult to know, to be honest.