I like it!

Besides the application for blog posts I think this would also be really useful for generating thumbnails for forum posts.

Indie Hackers does this really well - www.indiehackers.com/forum/ho…

I'm not sure if I would pay for that.

How about if for every 30 days you ship you get a shield. So missing a day breaks your shield instead of your streak.

That way longer streaks are slightly harder to lose and it's no big deal if you forget to ship 1 day a month.