Understood... and agreed. I've been playing with Drupal 8 and just tracking down an error message through the maze of Symfony and PSR0 routing is daunting. I tried to submit a 4-byte unicode patch and eventually my head hurt (and as it stand now, there's no patch in Drupal core for it).
The big issue with leaving it running is if anyone has an Ubercart install - as soon as EOL for D6 is declared, your Ubercart install fails PCI Compliance requirements because it is no longer being patched for exploits. If you're running a vanilla site, D6 is fine, but more and more I'm finding that a lot of responsive design components (say Flexslider or Bootstrap or Zurb or whatever) that you might want to use are off the table with D6 unless you use JQMulti which lets you run more modern JQuery, but it's complicated
One way or the other, I think most D6 users are going to be looking to upgrade in the next couple of years. The question is what will they upgrade to?