I think it's a good business case and a very well-written article, but it would be a good business case for just about any fringe sport you were trying to take mainstream. And if I were going to invest in creating a sports media empire trying to drum up and sell interest surrounding a sport, I'd probably pick one that has more than 1-2 exciting events per hour. Trainspotting is probably more action-packed than long-distance triathlon.
Which remains the big problem: You can create all kinds of interesting programming _around_ the sport, and leaderboards, and make people care about the individual pros, but it's still painful to the business case if the actual sport you're trying to get people interested in is still really, really boring. An optimum triathlete is one that _doesn't_ let their power fluctuate very much, or sticks to their race plan even when getting passed, etc. Live TV content (aka sports) is where the money is at nowadays, and live triathlon coverage (even if they produced it really, really well) is still going to not have much to talk about. Draft-legal bike racing is more exciting since you have attacks, changing terrain, strategic considerations, mid-stage sprints, and so on.
To compare to the other sports you referenced:
NASCAR: Has crashes every 10 minutes, people jostling for the lead, the perception of danger, etc.
F1*: Has the perception of danger.
Golf: Has a action->"will it make it?"->result cycle that lasts like 20-30 seconds. It's easy to get sucked into watching golf because you always want to know if player X's shot went in, and the moment that gets resolved, there's a new player's shot to follow.
Tennis: Very fast-paced, and divided into nice little discrete games that suck the viewer in.
*To be honest, as an F1 fan, it's probably the most boring "mainstream" sport, and when I try to get non-F1-fans to watch a race, I usually resort to "oh, you need to know the driver's backgrounds" like you're proposing with Pro's stories. There's not much passing, and serious crashes are usually only once or twice per race.
If I was going to invest in a digital content and media push to make a fringe sport/event/entertainment product popular, I'd probably pick online gaming like League of Legends / Dota / Heroes of the Storm. A match lasts 30-45 minutes, has lots of back-and-forth, is actually exciting, you can sell viewers the game so they can play at home, etc. Probably too late to get on the ground floor of gaming though. It's been big in Asia for quite a while, and is growing fast in North America. The prize pool for Dota2's world championships this year was $18m. And it isn't even the biggest game in that genre.
Athletically, there's plenty of exciting team sports that for whatever reason haven't taken off in the North America. Cricket, Rugby, Curling, even soccer might be better bets to try and make people care in North America.
STAC Zero Trainer - Zero noise, zero tire contact, zero moving parts. Suffer in Silence starting fall 2016