That's a good question, Gorgonkain. My comments in this thread were actually about the nomadic Light Cavalry / Elephants unit, so they'll be applicable to that.
I will admit something: I basically assumed that the Steel Bow Infantry (Archers / Elephants) were inferior enough that nobody would really want to use them or care! I also didn't take any look at the Ethiopian Skirmisher, Somali Skirmisher, Free Warrior, or Pictish Warrior on more than a superficial level. Part of this is just that I originally planned to do so (using them as archer-focused units), but then I saw both (a) how weak the best of the archer-focused units were and (b) how very complex and time-consuming it was to work out the blended archer compositions. The archers alone, even when I only covered the three types that I did (Nubian, Welsh/English, and Generic), took longer than anything else.
Now, what I hadn't considered is that someone might want to blend the Steel Bow Infantry with the Generic Defense retinue. That's interesting! Thanks for making the suggestion. When I have the time, I will take a look at that. (One of the problems with a Steel Bow Infantry archer-focused composition is how difficult it would be to get a Welsh/English commander, which is what you need even to get the sub-par results... but Defense retinues by themselves shine well enough. It's possible that a small blend of Steel Bow Infantry could enhance that. I'd have to check to be sure!)
So I'm saying I will have to get back to you on that. Thanks again for the suggestion.
Another unit type that I'll be looking at (which was not in the OP) is a Defence / Light Skirmish blend (as an alternative "lazy" blend to the 5 Defence / 3 Shock). And of course the Hussars (which were just an oversight). I might also look at the four mentioned Light Infantry retinues (Ethiopian, Somali, Free Warrior, Pictish) if there is any demand for it and/or any ideas on how to make them work (like this one about mixing generic defence with steel bow infantry).