There has been, IMHO, a great response to the new group. The first month has seen over 700 messages - averaging more than 25 per day! With some people predicting the demise of Usenet it is good to see a new Usenet newsgroup being so well used.
Of course, many people read rather than posting and there is no way to know how many of those there are. The only hint I know of is where Google reports the number subscribed via its Groups service. That number seemed for a while to stall in the twenties but has now reached
Google also report in the group descriptions that comp.sys.raspberry- pi has 129 subscribers. I don't know what they derive that figure from. Perhaps it is an estimate which combines unique posting ids and their own subscribers count. Just a guess. At any rate the total number of subscribers across different Usenet providers is likely significantly higher so it seems that quite a number of people are getting some use from the new group.