You can move 3D mesh points:
--move 3D mesh point
local mesh = moho:Mesh3D()
local vec = LM.Vector3:new_local()
vec:Set(0, .5, 0)
mesh:SetPoint(0, vec) --0 is pointID
But like you say, there's no channel to animate it. I tested this ages ago, and have meant to find a way to allow the user to select 3D points and manipulate them. At least on frame zero you could edit the 3D mesh.
And you can technically animate anything in AS. Just have to use the same trick I did to do animated shape sorting, where I repurpose a switch to hold the key values as strings (and a layerscript to use those values).