Currently i686 users are at about 1/6th of x86_64 users, by mirror
checkins. I don't have an easy way of knowing how many of those i686
checkins are old releases -- I'll need to ask Smooge to make a custom
report -- but I think it's fair to guess that it's significantly tilted
that way. So, taking a SWAG, I'd say maybe 10% of our users would be
impacted. That's pretty big, but on the other hand if the cost is
disproportionate If cost is an issue, consider to drop all these ppc, arm, s370 and mips

Their user base is like magnitudes smaller than the i686 user base, while these target are having a significant impact (and thus cost) on everything in Fedora.

Yes, but in the resource limited world, it's reasonable to support ARM because it's a viable, expanding platform, whereas x686 is obsolete and even you would probably agree that it is in attrition mode. Even PPC/MIPS/S370 aren't like that---there are active precisely because some people still make new ones. and are willing to invest time and/or money in them.