Wow, so many Ravenclaws! It's interesting, given all the INTJs on this forum, I'd think there would be some more Slytherins here. I feel that the INTJ personality tends to lend itself towards either Ravenclaw or Slytherin.
Among those who've posted so far, I see high percentages for Ravenclaw with secondary traits in Hufflepuff. Thinking about it, it makes sense given that this is a forum about early retirement.
Most early retirement seekers are clearly very intelligent, rational, and methodical, yet not afraid to think differently, which explains the high correlation with Ravenclaw. People with high Slytherin traits should be more ambitious, and therefore may be less likely to seek out early retirement. People with Hufflepuff traits ought to be less ambitious and more satisfied with what they've got, which lends itself well to exiting the rat race.
Personally, I find the idea of having the financial freedom to live my life in whatever way I want to be a very ambitious goal. Surely, having the power to be the master of one's own life, to pursue whatever interests you, to be beholden to no one, to live wherever you want, for as long as you want, to wake and sleep as you please--it's hard to find a more lofty goal to strive for! But maybe the other Slytherins don't agree?