I first want to agree that Mark must be able to run GIO effectively and with appropriate funding, it's his baby to orient as he wishes. The crux of the new funding proposal has to do with number of members, which is not unlike other list-serve plans.
I think the fear and push-back is coming about due to conditions like groups that have migrated away from the (totally free) YahooGroups, now defunct, but were populated by an awful lot of unofficial groups (not businesses or monetized clubs) that just wanted the members to communicate with each other. I actually do such a one on GIO, currently over 1000 members, on Premium. Many groups just want to talk, don't need fancy other features.
So, I wonder what specifically are the relative costs associated with some of the classes of features to see if were possible to have perhaps two kinds of Premium groups (or give them different names), one that has all the bells and whistles but more limited free membership (then pay for extras), basically the proposed new Premium group structure, and secondly the other one which would have unlimited membership with email/archives but no bells and whistles (though polls would be a natural fit here).
I'm guessing (unfortunately) that email throughput and server-power to handle that, bounces, and all related, is a major cost (if not the major cost). The actual definition of each member has to be trivial. Email archives are important, though as many mention/wonder if older archives need be maintained. I think it would be difficult to characterize this well and groups would probably rather keep old stuff than try and have a cut-off date. So, if the costs directly scale up with membership no matter what I don't see a way to solve the problem for large groups:
Basically I'm trying to find a Mark-palatable alternative for larger groups that aren't official anything, just groups of folks who now have a mechanism to discuss and share information, but nothing official, no organization, no monetization exists. Is it possible to continue to support such groups, new ones in particular, by a plan with a different feature set - mostly email oriented, not file storage and other things.
I will mention that my GIO group, like many, has a much smaller vocal set of posters than the full membership, and posts could easily average less than 10 a day. Since I wanted to keep us on the Premium level, yes to help pay for GIO, I put out a voluntary ask for small donations. I received enough this way from a sufficient small group (two-hands-full?) to pay for a year, and a bit more for next year. I can't possibly imagine any way to ask everyone to put in 55 cents per year, if we ever got un-grandfathered.
Of things mentioned in these posts, it seems reasonable to ask the entire membership once per year if they are still interested in being a member and if no response is received (after at least one more try), then delete them, to help trim membership and keep email handling down for the GIO system.
The whole issue of 501(c)(3) brings up entirely different stuff, and is not as simple as some posters may think (and then there is that question about non-US groups). I suspect that most groups are logically "non-profit" as they are just folks communicating with each other, no goods or services are sold. For companies that want to use GIO it's of course a different story, but then again they are monetized, "non-profit" or not.