-Is the group owner supposed, or is groups.io going, to maintain aNeither.
Well, actually Groups.io but not in the way you're thinking.
-What about restricted groups with a questionnaire - are peopleYes.
In my proposal the processing of pending members proceeds as normal, with the addition of telling the group moderator (in the pending email and in the Pending Approval tab of the Members list) of whether this applicant would need a group-sponsored slot, and if so how many such slots are available.
If a slot is not needed (the applicant has a paid account), or if one is needed and the moderator elects to apply one to this applicant, then approval proceeds as normal and the applicant becomes a member.
If a slot is needed and the group doesn't have any available, or the moderator elects not to apply one to this applicant, then approval makes this applicant an "inactive" member (that special status in my answer to Mark). Similar to NC status, the member cannot participate in the group (not even reading or receiving messages).
Like NC status this can be corrected after the fact. The member can correct it by paying for his/her account or a moderator can correct it by applying a sponsored slot to this member.
-Is the 14-day pending member limit (before deletion) going to beWith my scheme that needn't change: there's no new reason to hold someone in the Pending list; approve them with the knowledge that they may stay indefinitely inactive.
-In general, how and at what point, would or should requesting membersI'll have to think about whether the number of available sponsored slots should be shown in the group's home page and/or their directory listing. That would in some sense be friendly towards people with no means or desire to pay for their account, but it might lead to predatory behavior (over-subscribing to groups with available slots "just in case" or as a means of costing the group a valuable resource).
On the whole I'm inclined to say that the applicant finds out when they are Approved, and either become an active or inactive member. If the applicant is rejected then the question of available slots is moot, and they needn't have been informed sooner
-How, and this is not a technical issue, but how are group ownersMuch of the heartache with this issue is reduced in my proposal, because you can inactivate a member to free a slot rather than removing them. Inactivation can and should be associated with a Member Notice by which the group says whatever they think needs to be said about the circumstances. But the key here is that the inactivation can be cured easily by the member or the moderator without all the overhead of removing them and having them re-apply.
-"Try before you buy" also sounds very tricky. How many people will beThat's handled entirely by Groups.io. From the point of view of the group such people appear as paid accounts (no need to use up a slot). When their trial expires they go on Inactive status.
That event would be logged to the group's Activity page, and a group moderator can choose to receive a notice (like a "left group" notice). I don't know if it needs a separate control or just rolled into the moderator's subscription control for Members notices.