According to a press event in South Korea recently, Diablo 3 game director Josh Mosquiera may have revealed Blizzard's plans to use a League of Legends style pay model for their Heroes of the Storm.
Mosquiera had said those who pre-order the new World of Warcraft expansion receive the Demon Hunter for the MOBA, which would mean you'd need to pay to access heroes.
However, not only could the translation have been off, but such a pay model if it was going to be put into practice might only be planned for Asia, and not North America or Europe.
Blizzard has made no official statement with regards to their pay model with Heroes of the Storm. While Riot Games locks away heroes in League of Legends until purchased, Valve's DOTA 2 makes them all accessible but uses micro-transactions for skins etc. It remains to be seen which Blizzard will favour, and where.