There was some talk of it here earlier this summer.

Mostly positive.

You might want to PM Hardshell if you've got any specific questions.

The point was to get the range and velocity out of heavier .308 loads where a 24" or 36" barrel would be prohibitively long on a bolt-action or traditional layout semi-auto. In terms of design intent, the RFB was meant as a long-range DMR. I won't say "sniper" because they didn't knock themselves out going for that extreme level of accuracy.

With the right loads that will make use of the long barrel a heavy .308 bullet will perform kinda-sorta in spitting distance of .300 mag at long ranges like 500 yards +.   Kelgren and whoever else at KT  designed it approached it from the standpoint of making a long barrel useful and went with a bullpup to solve that issue, rather than "let's make a bullpup for the sake of making a bullpup". Obviously the only answer was to make it a bullpup, but it's still important to understand the thinking behind it's design intent to better understand the rifle.

While it looks ridiculously long, the 36" barrel RFB, if they ever made more than a prototype, still fits within the length of a 20" bolt action rifle.  That it's initial intent was as a precision rifle, "precision" being "man-sized targets" out to 600 yards and more, is also helped by the fact that whatever other complaints there may be about the RFB, that it has one of the best, if not the best factory trigger for any production bullpup rifle plays into this.

The 18" barrel carbine version came out first, and with the popularity of the 16" and 18" M1A's from Springfield showing that the market wants/likes short .308's/7.62's, I guess most people figured that was good enough, and Keltec was happy to make the 18" ones that actually sold the best, even if that wasn't the original intent of the RFB.

Once I'm done blowing all my money hedging my bets with NFA stuff in case rule 41p on NFA trusts goes into effects and it sticks, an RFB with the 24" "hunter" barrel is on my short list once I can get back to focusing blowing my money on bullpups.