I am not opposed to race plugins for my mod. Best example is Orc Fortress, which let to me myself writing Kobold Camp. I wholeheartely approve, and I am curious about the goblins, elves and drow that are on the way, and the maybe reavers, undeads, illithids and whatnot that are produced. I do however have some requirements, before I add something to the official Masterwork DF package. Anyone can write any plugin, no matter what, but that does not mean it needs to be added.
If the endproduct of this Human Castle plugin is well made, playable and fits the DF theme, I see no problem adding it. But if the manual and ingame files are in half-script-kiddy speak, I wont.