The alchemy daily cooldown
This trick really took off when alchemists were given the ability to transmute epic gems. The demand was huge, and the supply was thin. Every alchemist you had was another cut red gem on the AH, representing a decent daily income. Now the transmute for the best gems that people buy are not on a cooldown, so alchemists need to use their cooldowns on something else.
The most popular use for the daily transmute cooldown, Truegold, seems to be less obviously profitable on many realms. Unlike gems that sell to anyone who gets gear upgrades, Truegold mainly sells to people who are crafting gear, and more often than not, its consumption is tied to the production of Chaos Orbs. Truegold cooldowns sell for a couple of hundred gold at most, and they are often available in the auction house at close to the raw materials cost.
There are other nice niche markets you might be able to use your alchemy cooldown profitably on, but none of them will add up to more than a couple of hundred gold per alchemist per day. In fact, even the epic gem transmute didn't add up to more than that -- it just felt more profitable because in Wrath, everyone had less gold. Inflation, man. It'll kill you.
Any port in a storm
So my answer is that it's probably not worth making a bunch of alchemists; however, let's look at what's really being asked. Kaefera seems to want to invest time and money into creating a low-work, low-risk, "guaranteed" income. Let's look at some other professions and see if any of them qualify for good "cooldown mules".
Jewelcrafting is a candidate, simply because the JC daily rewards a token that can be directly redeemed for a Chimera's Eye. These are used by JCers for their JC-only increased stat gems, as well as for several BoE blues. These sell for anywhere between 100-500g, depending on your realm.
Tailoring is a very good candidate because tailors can make Dreamcloth, the Truegold of the dressmakers' world. There are several different cooldowns to make these, and it boils down to 5 per week. While the cloth itself is BoP, it can be sold indirectly by making and selling bags, spellthread, and a few epic BoEs.
Other than these, I can't think of much. Inscription has a dinky little quest you can do on a cooldown, but it's not worth the ink and probably never will be. Your best bet in terms of daily revenue would be a couple of tailors and jewelcrafters; however, I'd like to challenge whether this is actually a good idea.
Easy money isn't easy
Easy money is worth more than hard-earned money. We all have limits on our playtime, whether it's the number hours we can stay awake after chugging two gallons of Mountain Dew or aiming to spend more than 80% of our "free" time with our family. In addition to the actual gold cost of leveling the profession, everyone needs to factor the investment of time required to get a business started into their decision.
The biggest factor in your decision is going to be centered on leveling all those characters. Assuming you don't take much less time to get a non-death knight character to 85 than I do, this represents the single largest cost in setting up something like this. At first glance, it seems like leveling these guys is something you wouldn't have done otherwise, and therefore, I'd recommend that you compare the revenue that you'll make with your cooldown mules to the revenue you lost by spending weeks and months of valuable playtime frolicking around in Feralas.
That said, one of my biggest competitors (also a good friend and officer in my guild) has a bunch of level 85s, and he would likely have them whether he needed the profession slots or not. If he were comparing the value of nine cooldown mules, he wouldn't need to consider the time spent leveling characters, because that's something he'd have done anyway. When I do this math, I do need to consider it, because I have exactly one max-level character and will never have another one unless it can't be avoided. If you're not the type of person who will play through the same soul-crushing grind to get all your characters up to at least level 75, you need to count the time spent doing that.
... at least?
There are eight crafting professions, a couple of which require level 84 to get to the good stuff. The lion's share of the profit from most of these professions comes from the production and marketing of cooldown-free items. The optimal setup for the non-cooldown portion of business is one of each character of the minimum level possible to achieve the desired recipes. Load stuff like blacksmithing and enchanting onto the same characters so that you need to get as few characters to 84 and into Twilight Highlands as possible.
Just so we're clear, so far, we're at four characters, and only two of them need to be level 84. Every character after this has two primary professions, and assuming you give each of them some combination of tailoring (if you're willing to level them to 84), alchemy, and jewelcrafting, that represents a cooldown that you can log into every day.
Every single cooldown mule has to be justified by the cooldown revenue and possibly the pleasure of running a toon through Stranglethorn for the ninth time. The revenue isn't unlimited, either. It will last until the end of this expansion, at which point the only lasting value it will have is that you won't need to level a character again.
If you have characters with free profession slots, don't feel you absolutely have to fill them. Once you have the ability to make everything, the time and money you spend working on these duplicate professions could also have been spent working on your other crafting professions. It may be easier to move into the bag or BoA enchant market than it would be to level yet another jewelcrafter, alchemist, or tailor. Basically, unless you feel that you have the market for your current tradeskills so well nailed down that you'd be wasting time trying to get lower costs or higher sales, stopping to level a mostly duplicate tradeskill is a clear loss in money.
Admittedly, cooldowns are easier, but figure out how many weeks you need to break even if you're at 4,500 gold per character per week. If it's worth it but you don't yet have a character capable of learning these cooldowns, consider how much money you could make in the /played time it can take to get a character to your target level.
Maximize your profits with more advice from Gold Capped as well as the author's Call to Auction podcast. Do you have questions about selling, reselling and building your financial empire on the auction house? Basil is taking your questions at email@example.com.