It should end when XP's market share is vanishingly small. Given that as of a couple weeks ago it still has 27% among Windows users [1], we are nowhere near that point. Microsoft should do everything they can to help customers, especially corporate users, upgrade to the current version. Presumably they're already doing this, but in the meantime they should continue at least providing XP security updates given its sizable user base.
You have been warned about XP's end of support date for several years, on top of it corporate customers can buy updates directly from MS. I'm not seeing the problem, other than the public being irresponsible, which no corporate policy can cure. We can extend support another 6 months and be in the exact same place. There's no winning here.
I also find it hard to believe those old XP machines aren't compromised already. Worst case scenario is that they leave one botnet and join another.
Also, those stats are from web user agents, many bots use XP user agents, so we really don't know how many XP machines there are. I imagine most are corporate for compatibility reasons and are receiving patches. The rest are irresponsible people unwilling to upgrade and probably aren't running updated AV either.
At the very least this can be an opportunity to scare people into upgrading or at least switching to a non-IE browser and making sure their AV is up to date.
tldr; can't save the world and you can't save people from themselves
The point of the previous EOL extension was this, basically. What Microsoft figured out was that XP's market share was not going to appreciably shrink unless they let it finally reach end of life.
