Whether you can enchant a Black Blade is settled, to the best of my knowledge, but is there any official ruling on whether you can have a Black Blade made out of special materials?
Primarily looking at Wyroot.
The first question to ask\answer is: Can wyroot be used to make a functional "one-handed slashing weapon, rapier, or sword cane"? Wood doesn't tend to hold an edge very well, so I don't know if it would really be allowed per RAW. I think wyroot would be more appropriate for a weapon wielded by a staff magus, since a quarterstaff is normally wood.
As to other more appropriate materials for blades, I don't think there's an official ruling either way. My gut says it probably wouldn't be allowed, but from a perspective of current RAW it would be a GM call.
Whether you can enchant a Black Blade is settled, to the best of my knowledge, but is there any official ruling on whether you can have a Black Blade made out of special materials?
Primarily looking at Wyroot.
Because I want to see it.
Where was it settled ?
James Jacobs chimed in on it in a thread here. I thought that either JB or SKR had as well but can't find it now.
Whether you can enchant a Black Blade is settled, to the best of my knowledge, but is there any official ruling on whether you can have a Black Blade made out of special materials?
Primarily looking at Wyroot.
The entry for wyroot in Ultimate Equipment is pretty clear: "Wyroot can be used to construct any melee weapon made entirely of wood or a melee weapon with a wooden haft." Also, with wyroot as the main component, the weapon deals no damage on a hit.
Otherwise, there are no rules specifically limiting black blades from having special materials, but a GM should be wary of giving a black blade expensive materials at 3rd level, simply for WBL reasons.