Most conventions offer a "Longtimer's Only" meeting which packs the room. The sobriety time requirements vary, of course, depending on location.
Some areas have meetings that are strictly for member with a certain amount of sobriety time and up.
Some groups never ask for volunteers and only call on people, often calling on the same people again and again. Some groups use Red Ball method, where the person sharing picks the next person sharing. Some groups have a policy of 6 months sobriety to chair a meeting. Some groups actually state.....please listen if you have 30 days or less of sobriety.
These practices are up to the group, decided by group conscience and, therefore, quite OK. Groups are autonomous.
I personally enjoy getting to know newcomers, and that's why I call on them to share. And most people are reasonable, catching onto a 5 minute timeframe.