I did a pass through the consensus to find relays with old versions and working contact info and consensus weights >= 100, to let them know to upgrade.
There are a handful of very fast relays with old versions and no contact info.
Looking at things as a percentage of the network is not the whole picture, since 4.7% of 5121 is still 240 volunteers that we are effectively telling to go shove it. As the network grows, the number of real volunteers grows too.
But all of that said, I recognize that keeping relay versions sufficiently up-to-date is necessary too. Hopefully some of them will upgrade.
Are we sure we want to cut out 0.2.3.x for x<25 also? The consensus currently still recommends 0.2.3.24-rc so I think we will want to be more lenient here.
Looking over the changelog, I think 0.2.3.16-alpha's fix of #6033 (moved) makes that one a plausible "not below this one" cutoff. Other ideas for cutoffs?