@Kowlin Thanks 
We're thinking of replacing a 10 year old vBulletin site where the average user age is very high. There are some users who still uses IE7 and IE9. I never support IE7/8 on any of my sites anymore, but IE9 is usually still a "maybe".
I'll discuss this a bit more internally before we make a discussion. NodeBB seems really nice though, and is our current favorite. The replacement is going to go late fall, so the outdated browsers will be even more outdated by then...