Like I said, the carriers probably have a lot of influence over it, they certainly did over hbo until hbo told them to go eff themselves and nothing negative happened to hbo on cable. Hbo gets more money per direct now sub than they do per cable sub.
Being a cable sub service makes it a bit of a bad comparison though. I think you're right that espn probably wouldn't gain enough app subs to offset the likely lower carrier fees. But is it certain those would go down?