arent there sora triples still being sold now, front derailleurs I mean? I would think that this would work fine, check out the trek 520 that has 9 spd sti on it I think.
My tiagra 9 spd sti and tiagra triple fd works great, and the newer sora sti shifters seem very much to be a trickle down of the old 9 spd tiagra, and they work very nicely. I bought and put a pair of newer paddle sora sti shifters on my wifes bike a few years ago, and they feel rather nice. Way better than the thumb shifter 8 and 9 spd soras imo, having used both now.