After prolonged deliberation, the thread of the year has been selected. It wasn't made this year. In fact, that's why it was selected. It was selected because not only is it one of the forum's more interesting challenges, but also because its creator has been actively maintaining the challenge for over five years. That's right: the thread is nearly as old as the forum itself and is still going strong. And the winner is...
Congratulations to @boolybooly, and more importantly, thank you for your long-term commitment to supporting and entertaining the KSP community.