We are nearing the end of Jade Regent with two players and four PCs (each player has two). If you have two players who can make clear roleplaying distinctions between the PCs (not a problem in this game) this works fine.
We are halfway through module 1 of Jade Regent with one player. He is playing two PCs (a level higher than usual) and there is a party NPC. I plan to be somewhat more encouraging of recruiting Spivey, Ulf, etc. than the GM of the first mentioned game was, but it's a delicate balance--I bog down as a GM if I run too many complicated people in combat. I may have to ask him to do an NPC or two at some point.
In the second game the player is essentially playing the Ameiko role (we don't have Ameiko and her group)--it'll be interesting to see how that works out. Of course I had to delete the kami subplot in module 1, as it wouldn't do to put one PC out of commission for half a module.
I also reset the game to start geographically in a village in the Forest of Spirits: it will go north (putting Ravenscraeg in the Hangul lands, and giving the PCs a quest to go to the Crown rather than to cross it) and then back south. I've felt that the biggest artistic flaw of Jade Regent is that it's supposed to be about Minkai but takes a really long time to get there, so the PCs never get a good sense of the place. I hope the resetting helps. So far it's not hard.