It would be cool to have a function for drawing triangles in 3D world - something similar to what dxDrawLine3D does with lines. The function could be something like:
dxDrawTriangle3D(x1,y1,z1,x2,y2,z2,x3,y3,z3,filepath,u1,v1,u2,v2,u3,v3,c1,c2,c3)
x1..z3 : coordinates of triangle vertices in GTA SA world
filepath : texture file for triangle
u1..v3 : UV coordinates for each vertex
c1..c3 : color of each vertex (like color in dxDrawImage), interpolated for every pixel.

Such function would allow us to have unlimited number of models with dynamic shapes - something what we can hardly achieve with DFFs. Sometimes it may even be a bit wasteful to use DFFs.
Examples of possible uses:

1. Ped DFFs can't be replaced yet. But if we had dxDrawTriangle3D function, we could set ped alpha to 0, calculate positions/rotations of the bones and draw a custom model around them.
2. My drawtag resource ( http://www.youtube.com/watch?v=9eR25dEwLQ8 ) uses a slot for a generated TXD. There can only be one tag texture. It's possible to improve the resource to have more textures visible at the same time, but then they would take more model slots. Using dxDrawTriangle3D, we could make MTA draw custom tags without wasting model slots for simple rectangular models :)

Though I don't know if this function would be fast enough...