I think my answer to your previous topic on this still stands:
But to try and pull this back on topic for this topic, the ‘powered by Discourse’ addition is fairly new and we are exploring different approaches to enabling it. We may well start enabling it by default for new sites, but we’re mindful of the impact it could have on existing ones. However, as it is fairly easy to turn off this may also be an option too.
If our approach on this does evolve then we’ll post an update in the announcements topic - New feature: Opt-in to display that your site is Powered by Discourse topic