Lolbash, I think you're a bit too focused on the word 'knight' rather than the context it was used in. I could be wrong, but I believe what was being asked was not the ability to be knighted, but rather having more steps to being welcomed into a faction's elite classes. Instead of calling it being 'knighted', we could call it 'commissioned' if you prefer. For example, you start out, raise a small warband, and take out some bandits. King what's-his-name from Vlandia takes note and hires your warband as mercenaries for his campaign against the Battanians. You perform well, but don't do anything that particularly stands out (taking a castle/town yourself, taking on a much larger party as a distraction, etc.), but after 'years' of loyal service he offers you a commission. Basically, he's accepting you into the faction w/out making you a vassal, but it's another step in that direction. It would pay more than being a mercenary, you'd get more quests/contracts dealing with internal rather than external threats, and maybe you'd carry the king's/lord's banner (the one who commissions you) rather than your own. After a while of doing that successfully, you could be offered full vassalship, with your own lands, banner, and everything else that comes with it.
This would increase the amt. of time spent earning your way to nobility w/out making the player feel stuck, as there is still some progression involved. It would also put more emphasis on land-owning as a later-game feature, meaning that hopefully you get less bored of owning fiefs because you have less time to sit around and protect them, or watch them get sacked over and over again.