It would be interesting to have a Silo in the middle of the cavern on Walls because of there being four vantage points either faction could take advantage of. (Ground, walkway, top of the cavern and ariel)
An underground silo in the sub-tunnels on Islands would be tricky but also interesting.
I suppose on the cliff edge just below the bunker on Volcano would be an interesting place to put a silo, access via a steep stairway from above and below for the infantry making for some interesting tactics.
These would just be interesting. (to me)
On a whole, I quite enjoy the extra dynamic the silos add to the game so much that it's refreshing, something to fight over is always nice.
Like C&C_Walls_Flying and C&C_Walls from Old Renegade, perhaps (for example) Renegade-X may require to have CNC Under and CNC Under-NS (No Silo).