So every faction has 4 experimentals (and Aeon actually has 5. The rapid fire artillery is a definite game-ender and should be counted as experimental in my book), but Seraphim only has 3. Seeing as they have a land, air and (indirect fire) building exp, this fourth experimental would be a naval one.
Now, I'm pretty sure this won't ever be included in the full game, but I would just like to discuss what the fourth exp could be, because I honestly have no idea. But anyway...
The UEF naval exp is an submersible aircraft carrier, the Aeon one is a submersible battleship and the Cybran one (Megalith) is an amphibious unit. So they all work on different layers. To mirror this, the Seraphim one should work on different layers as well. The only ways to do this that would be unique is if it would be a naval unit that can fly or if it is a land unit that can float onto the water.
Thoughts?