Hello axis.
There are already several types of 'non-specialist' specialists, these are mostly at the moment generated from luxury food, (some civics do change the normal food 'birth' as well) but we also have talked several times about reintroducing the 'journeyman' concept where a peasant can gain experience and become a non-specialist specialist who is just a bit better.
We have also talked about a much more in depth system of non-military promotions, education and experience gaining.
"Why “wily trader”? Why not simply “tradesman” or “itinerant merchant”?"
You realise 'itinerant merchant' is longer and less simple than 'wily trader', so the question for you is why not 'Wily Trader'?
Veterancy:
We do already have some veterancy in the game. (although we are planning a major overhaul of combat/military)
But what we currently have is untrained, trained, and I think it is 'honoured'.
Trained troops have access to several professions that untrained do not (for example archer and longbowman) a unit can only become a knight if they are honoured and usually only Nobles recieve it under certain civics, but I think it can also been gained through combat. (I forget exactly the nuance of the system it has been a while since I played)
Military Professions:
We do more or less already have all of those. Horse archer I think we might not have at the moment (not 100% sure) but the mongols are growing in presence within the talk and design, so if not it will be soon I am sure.
I don't know if we have a ranged skirmisher, at the moment we have armed peasants and spearman(infantry? I forget the name) which are the entry level soldiers, then archer is the entry level trained soldier (equipped using tools rather than weapons).
We have skirmisher and heavy skirmisher.
We have swordsman and pikeman (which could be classed as the medium and heavy infantry)
We have horseman and heavy horseman, Knight and Heavy Knight (we are also talking about the idea of horse armour/armoured horse as an equipment resource)
We already have archer, Longbowman and Crossbowman.
We have 2 kinds of catapult (we do talk on and off about moving things like this from a built vehicle to an equipped profession to require a pop unit to take it in the field so that could be the siege engineer)
Each of our military units also have sub divisions for armour type and equipment type (weapons or tools)
So we actually, as I said at the beginning, already have more or less everything you suggested, and probably more than twice that.
Resources:
Yes, many if not all of those have been considered, in various forms and functions. Some you could say already 'exist' in a 'clumped form' as we have spices(cinnamon, cloves) Luxury food/food (honey, fruit, we have also talked about the idea of apiaries creating wax and or honey)
We have Ore (Tin, Copper, we have also talked about these being bonus resources, and also a system of getting special benefits when you control different kinds of bonus resources in World History Mod discussions, I put forward the idea of ore being smelted into various metals for various uses, but that was stretching across a much wider time period and not necessarily as useful for Medieval only)
We have also discussed rope (primarily in relation to a ship building resource).
One thing with adding more yields, is figuring out a good purpose for the yield, right now most yields are only there to make money, and a lot of the time you only need 1 or 2 to make money, so there needs to be a game mechanic reason for something more to exist.
We have loads of yield ideas and suggestions that we rattle out every now and then, the hard part is finding the reason (game play wise) to bother putting them in at all.
What will motivate the player to actually build them. (we have talked about making markets more susceptible to flux, and thus diversification will be needed to keep up your trade economy, but we already have several things that can be diversified, so would more diversification add much more game play? That is the current debate.)
So as you can see most of what you suggest is actually already in game, (that which isn't is more or less planned in some form or other) the hard part with this is not so much coming up with historical stuff, but actually the game play around that historical detail to give a reason to add it in.
Then also the time and effort it takes to add the stuff in!
Read around some of the sections though and you will get a sense of the sort of things that are planned/coming or being tested.