If you're interested in the impossible, let's just say that it's been an interesting week.

First there was controversial news at Burger King. Then, there was news about how there's next to no news news at all at McDonald's.

But now, Subway might have the most important news of all.

Let's start first with reporting by my colleague Chris Matysczyk, about the surprising thing Burger King admitted this week -- namely that it's preparing its plant-based Whoppers "in the same broiler used for beef and chicken."

Hardcore no-meat-eaters aren't exactly thrilled about that.

Meanwhile, there was just the faintest hint that McDonald's might be getting on the meat-less meat bandwagon in the United States.

As my colleague Peter Economy reported, Impossible Foods is reportedly working with a food supplier that in turn works with McDonald's -- suggesting there might some kind of meatless meat coming to McDonald's at some point in the future.

But now, like a dark horse contender (sorry, horrible analogy), it looks as if Subway is racing to the front of the pack.

Starting next month, the world's largest restaurant chain says it will be offering a meatless meatball sub, after teaming up with plant-based meat substitute company Beyond Meat.

I don't know which will be more surprising to people: the idea of a meatless meatball sub, or the simple fact that Subway is so much bigger than McDonald's and Burger King.

Let's take the second point first. The tale of the tape as of 2018:

42,431 Subway stores;

37,855 McDonald's restaurants; and

13,000 Burger King restaurants.

It's fascinating. If Subway were a TV show, it would be NCIS: extremely successful, even though it's not exactly socially popular. (It reminds me of how people failed to predict the electoral victory of President Trump.)

We don't know exactly how well Subway does as a company, since it's privately held. But it is an amazing and inspiring entrepreneurial success story -- founded 55 years ago with a single store.

Still, for a while, it's seemed like it just hasn't kept up with consumer preferences.

As one retail consultant put it to The Washington Post: "Let's face it. If you're in a major metropolitan area, you're looking for that green salad place. You're not saying, 'Let's all go to Subway and order through the sneeze guard.'

Now, however, we're reminded: Being hip or trendy doesn't make a successful business. Ultimately it's all about real, cold, hard numbers.

And that's why, even though the meatless meatball sub is just a test for now in about 685 of these Subway restaurants, Subway's larger size perhaps means it has a much better chance of catching on more quickly than its smaller competitors.

I have no dog at all in the fight over meatless meat (sorry, another bad analogy). By that, I mean that I like to eat meat, but I also enjoy really vegetarian options.

Personally, I just don't see the need to create a plant-based meat substitute designed to fool people into thinking they're actually eating meat.

Even in places like Sweden, they apparently find that weird.

But if you're betting on whether companies like Impossible Foods and Beyond Meat really have a long-term future, for now at least, I wouldn't be watching McDonald's or Burger King.