It's in Gentoo's portage, and I'm pretty sure that it is in Fedora's repos. It's probably in many of the others' repos, too. I'm sure it isn't installed by default because 99.9% of all users don't really care about the text consoles. (I'm in the 0.1% too.) I also think you have to login through a getty on a normal VT and start fbterm as a normal user. You can't have fbterm running the getty so it can't be integrated the way most distros would like. Although, I could be wrong about that; I'm no expert.
Oh, I just noticed fbterm is in the Debian repository (hence Ubuntu and Linux Mint too).
Originally Posted by signals
As I understand it (someone correct me if I'm mistaken) kmscon is a work-in-progress to replace the kernel's VT code with something that uses kernel mode setting to manage the display hardware. In its current state, it doesn't actually do any terminal emulation, but they're working on it. fbterm is a user-space program that draws to the framebuffer and is already a fairly complete terminal emulator.
kmscon wants to get the in-kernel VT removed and replace it with a user-space VT.