Not only have we not come up with a solution, there might not be one:
Co-winner of the IgNobel prize for Physics, shared with the British researchers who discovered a formula for the optimal method of dunking cookies.
I’m sure that Dyson will perfect the spout at some point, and that that will be the end of it.
A Sheldon Comic that speaks to this problem.
Coffee is “one specific liquid.” And while different individuals might pour at slightly different rates, I’d guess that most people’s rates are within a certain small range. Therefore, while you may not be able to create a perfect spout for a mass-produced coffee pot, you should be able to create a reasonably-close-to-perfect-for-most-people spout. Or at least one that doesn’t suck.
Ahh, come on. He’s not even built that fucking sphere yet, and how long have we been waiting?
I heard it was suppressed by Big Towel.
Who will no doubt be thrilled by the fact that there’s laugh-spray tea all over my monitor.
To expand on what Green Bean said, 95% of liquids you’re going to be pouring out of a pitcher are going to exhibit the same properties as water, for all intents and purposes. Also, somebody with manufacturing experience correct me if I’m wrong, but a shape that’s simple, without being “regular”, if you will, still has to be designed, cast, and made into a mold. If there’s any extra cost, it’s going to be in the design phase, not the manufacturing phase. While I recognize that very complex molds can make manufacture difficult, and therefore more expensive, I don’t believe the perfect spout’s complexity approaches this threshold.
I peed a little. 
That’s what I came in here to post. I love Kellet’s rants on coffee, and this is one of favorites. A variation on the theme.
Maybe she’s holding your handle the wrong way?
“Here’s is my handle. Now watch it spout!”
Props to the OP!
That being said, it occurred years ago to my amazingly keen intellect to place the second cup where the runback would spill into it rather than onto the counter or myself. Absent the need for a second cup I simply preposition a paper towel to catch the mess.
*returns to meditations and solving world’s unsolvable problems
Crate and Barrel has a pouring widget that has a double-lip design so that you pour wine, and the drip is caught by the second lip, which feeds back into the bottle.
Presto, no more annoying drips that run down the side of the bottle! I’m not sure why teapot mfrs don’t do that, but I will note that the widget was backordered for over a MONTH from when I first ordered it.
Our tea kettle of many years has been lookking pretty decrepit for a while, and it needed replacing. My major complaint about it is that the damned spout can’t cleanly pour the hot liquid. Every time I use it to make tea or hot chocolate or whate ver, the hot water burbles out and a lot of it invariably missed the cup or mug, creating a little near-boiling sea around the cup.
So I was delighted when Pepper Mill got a new one a couple of days ago. Until I saw it.
It was Exactly The Same Model. After all these years, I’m amazed that she could find exactly the same one. But, considering the problems we’ve had with it (and she has them, too), I’m doubly amazed that she bought the same thing.
“Why?” I asked.
“It was only five bucks,” she replied.
The answer to all your problems might lie in the acquisition of a thermal carafe like the one at:
(I bought one some months ago. It solved the fucking spout issue for us, but that was a side issue at the time. I just wanted to keep the fucking coffee hot.)
It has a good-sized hole at the top into which you can pour your tea, coffee, hot cocoa, tequila, etc., into it without splattering it on the counter. Screw the top tightly, and the liquid will keep hot (or cold) until the cows come home.
Examine the top of the top when you’ve screwed it tight. It’s jet black, but if you look carefully, with the spout at 6 o’clock, you’ll see the word POUR at 9 o’clock with an arrow pointing at the “9”. Now, spin the top counterclockwise 1/4 turn until the arrow points at 6 (and thus, at the spout as well).
Pour. No splatter
Now, if you’re especially stupid, cut a small square from a white 3x5 card and scotch tape it directly over the previously mentioned arrow. Then no matter how incredibly dense you are, you’ll always line up the POUR with the SPOUT.
Works for me. 
There is cost associated with manufacturing in the case of quality control. If the “perfect spout” has a high incidents of breakage during manufacturing, or has a shape that causes unacceptably high thermal stresses when rendered in tempered glass, you go with a different design or your increase the price of the finished product to cover the cost of all that failure.
It may also be prone to breakage during use or not aesthetically pleasing to most users. So you have an ugly teapot that you hear breaks (but doesn’t drip!) or some other teapot that’s less ideal from an engineering standpoint, but works well enough. The perfect spout may not sell well enough vs. traditional imperfect spouts. Plus, it’s hard to get fancy and daring with your design if you have to have the same perfect spout.