Allright, since I'm apparently not distinguishing who I am talking to enough...
longish post
Only the early part of that post you were responding to was actually talking about what you had proposed, as I was splitting my attention between what you had proposed and what Silverionmox had proposed, and I had more disagreement with what Silverionmox had proposed than with what you had.
I had assumed "containers" referred to boxes/coffers/chests/bags, because that is what DF means when it uses the term "containers".
I'll respond to the interface in the next part, collectively.
What you were proposing, with a more minor sub-skill system, while I am less opposed to it, I still think would be better served with at most, simply using a "perk" system, where a single notable benefit is available for the player to see for a "specialization", rather than simply making you have multiple bar graphs of experience points that will likely do little to influence your decisions, anyway.
That is, if you have a carpenter who has legendary+5 carpentry skill because you shut him up in his workshop producing bins, barrels, and occasionally beds from here to the day he dies of old age, then does making him "Legendarier" in making barrels really net you much? If you wanted, for some odd reason, a wooden table, and wanted it high quality would you want anyone else making it if you had no other seriously trained carpenter? If it doesn't make any impact on your decisions, then it's just extra little pretty bar graphs, unless someone really wanted to pump out a ton of tables and chairs and bracelets because he
's gotta catch 'em all wants be the next Morul, and have every single bar graph filled out.
Then that's the problem, and will continue to be the problem regardless of the status of suggestions like this. We all know that this is a complex game that will continue to grow in complexity, and the solution isn't to prevent new features simply because the UI is bad, the solution is to bug Toady to rework the UI when the game grows too complex for the current one to be sustainable. He seems to be heeding such advice more these days, and we can be fairly certain that interface developments will occur.
Hell, look at what he's done with attributes: Those got more complex, and as a result they're being split into organized groups for the purpose of user-friendliness.
The first step, then, should be to ensure that such an interface would come before assuming it.
This, however, is only addressing one half of my problem with the proposals. The other half is whether or not that information actually helps the player. There is such a thing as data overflow. Just play a Koei game, you pretty much play by spreadsheets, and the trick of the game is simply knowing which bits of data are actually worth reading.
I would allude to an aircraft cockpit, but I think, rather a car is a better metaphor. If your car had information on how long your tires had been driven, the viscosity of the lubricant in your engine, the windshield washer fluid levels, and a few dozen other things thrown onto the dashboard, would you really be reading all those things when you were driving? For that matter, do you even look at all the instruments now, or do you mostly watch the road, and occasionally glance at the speedometer, without worrying about the RPMs, and only checking your fuel if it is a convenient time or your engine heat if you think it might be a problem?
This leads me onto my next argument...
The evolution of this thread is typical, the OP proposes some rather modest complexity incresse (Splitting a Cooper skill off of Carpentry) and people object or support it for legitimate reasons but quickly other people start throwing around additions that inflate the complexity. Different additions inflate in different directions and are not in and of themselves that bad, but quickly they seem to all get mashed together into some giant Frankenstein of an idea with exponential complexity and people start running with a debate on the pro's and con's of this giant new system with the complexity lovers embellishing it along the way and the complexity hates doing the same for straw-man purposes. Eventually the whole thread is derailed. I'm as much to blame as anyone else though 
I am not opposed to "Complexity" per se. I am not even opposed to "Realism" per se. I would like to see complexity and realism in ways that make the game behave in ways where Dwarf AI was not "stupid" or "suicidal", forcing players to use exploits like zoning walls to prevent dwarves from walling themselves into closed spaces and starving to death. The problem is that complexity and realism shouldn't be goals, what matters is (sing along, everyone) what change it makes to the way the player goes about playing the game. Adding complexity in a way that can only result in either forcing the player to micromanage individual dwarves' workloads so that they have the right kinds of experience in several specific sub-skills is not likely to be making the game any more enjoyable for someone who runs a large fort, and already has too much micromanagement to deal with. If this is minor, and the player never has to care... then why do this at all? Complexity is fine IF it lets a player focus on what he wants to focus upon (generally, designing a fortress, or a megaproject, or not getting eaten by ravenous hordes of zombie whales), but not if that complexity is translated into spending your time looking up data in a chart so you can figure out which flavors of experience your dwarves need more of as part of their balanced
breakfast workload.
As an aside totally addressing Impaler: This isn't a strawdog argument when I'm actually rebutting what someone else has proposed directly. (Also, isn't waxing philosophical about the reasons why things keep falling apart so that we can argue over that, as well part of the death spiral, too?)
Everything will ideally be modifiable in the end so if you don't like subskills you can just move everything you can do with the skill into the same category, making it the way it is now.
Hopefully the system will be robust enough to tune individual synergies. For example, you could mod it so making a barrel gives no XP for anything else while making a table gives you equal skill for chair-making and half the XP to cabinets up until it reaches rank 4 or whatever. Changing whether making a rock chair gives you XP in making wooden chairs is also important. Synergies between metalsmithing skills might be handled with proficiency with the metal itself, allowing greater than normal skill in it if cross-trained in other fields. Makes it every bit as complex as the players themselves want it
Yes, hopefully, we'll be able to mod everything we want to our own heart's content... but that doesn't mean that people won't, or for that matter, shouldn't argue over what becomes "standard".
It is also, like the interface debate, neither here nor there - you're pinning all your hopes or argument on a hypothetical.