To me, this becomes more interesting with a single topic everyone writes about, i.e. "Imagination". — hypericin

I agree. But the consensus was that people would participate more if the topic was left open. *shrugs*

It would be interesting to see how varied everyone's approach is, and how much richness there really is in the topic. — hypericin

Exactly this. From a wide spectrum of perspectives.

every writer deeply engages with the same topic, and only after everyone has written do they come together and discuss each other's take — hypericin

It is designed to be as interactive as the Literary Activity. The idea is to challenge ourselves, as you say, to dig deep. Or some will already be comfortable.

Similar to the Literary Activity, each author is initially anonymous. Readers respond to the writing. A discussion initially without the author. Waiting a week or so, depending on amount of entries, before guessing the author.

Authors can participate as readers in threads not their own.

Then, the authors join in their own discussion thread, responding to feedback. Also, engaging with other authors. It should be an exciting interaction, weaving questions, responses and trying to understand the meaning of the text.
Of mutual benefit in a positive engagement.

That's the idea...