There are several things going on here, that would make/break such a proposal. Many have brought up that the length and breath of internet access across the U.S. in general, is really pretty piss poor. So even if we're talking DirecTV level of HD distribution (say 8-10Mb/s for a single channel) that is about double what even 50% of people have access to, either through DSL or cable.
And of course, there's all the 'caps' and such, and the cost of that access. Which brings up the second big thing... cost.
Now, one can figure that the 'Wrath of Khan' pricing model will perhaps come into play. And what, some are probably asking, what the **** is 'Wrath of Khan'? Of course, the move (1982). But before it was released on VHS, the 'typical' movie was selling at between $50-100 or thereabouts in the market. Paramount decided that they wanted to 'goose' the sell-through, and priced 'Khan' at $29-35 or so (can't remember exactly what it was) but about 1/2 to 1/3'rd that of a typical VHS movie.
Folks came unglued. It was 'sold out' across the country. Paramount made a killing. A light builb went off over their heads, 'hey if we drop the price we make up the amount we wanted to in VOLUME'. No ****. Marketing 101.
So, here we have NFL/ST, but no real way to market it in volume across the Internet 'as it exists today'. Through DirecTV you have 100% (or close to it, obviously there are places in big cities with coverage problems just like there is way out west with those things called 'trees'). But it's pretty close to 100% coverage. If folks want it today, they can pretty much get it anywhere.
Until Google wants to fiber-wire the whole of America (in lots of places they will be barred do to EXISTING laws and regulations in states and municipalities), and a few Trillion bucks later, they can do what satellite does.
Really, DirecTV is cost effective against most cabelcos anyway, so as I pointed out, it's already at 99+% (potential) penetration anyway. And as to huge bandwidth folks like Google Fiber, FIOS (both Verizon and Frontier), I don't understand why they don't partner with DirecTV and forget about running their own 'TV' service, which they are at a distinct disadvantage to the huge cablecos (Comcast et. al.), and put the DirecTV bitstream on their fiber service.
DirecTV already has IP based DVR/Receivers running on large apartment/condo complexes around the country, it would be a minor bit of engineering to junk their current problematic 'tv service' and go with Direct.
But meanwhile, folks on internet service through other vendors, forget about it. You think folks like Comcast are yelling now with the pitiful amount of bits flowing through their service because of Netflix? This would really get them going at hyper levels.