Fans can watch the world feed but that could easily be done in any setup the Diamond League struck.
I think this deal shows the sad state of track and field in the country right now. The Diamond League essentially is giving up no trying to grow a fan base in the US with this deal. On what I regard the biggest stage of track in the Worlds (outside of the Olympics and Worlds) they are saying, "we don't care how many people watch in the US, let's just make a little money on this."
Makes sense short term but long-term do athletes want to compete where they won't be seen in their home countries? The counter argument is that the DL wasn't on TV in great numbers in the US to begin with so might as well make a few dollars.
My general take is Flotrack doesn't increase the audience of what it broadcasts, it sometimes increases the amount of revenue extracted from the broadcasts. Which has some benefits.
A few years ago, Flocasts struck a deal to broadcast DC United (MLS Soccer games). When the deal was announced DC United talked about how fans would get exclusive behind the scenes of the club as well as traditional coverage. (Note with this track deal there is none of that, Flotrack presumably will just take the world feed and charge you to watch it).
Nonetheless the deal was canceled halfway through the first year. The Washington Post said, "the exclusive streaming service damaged United’s momentum in the local marketplace. One season after rejuvenating its brand and popularity with Wayne Rooney’s arrival and Audi Field’s opening, United was largely out of sight and out of mind."
Now, for soccer fans were only paying $8.99 a month. The model with track fans is to charge a lot more.
The question is what the DL gets in return?