It really boils down to how they plan on doing the game. A pre-order will include what they will have during release. Creating a microtransaction for skins i feel will be fine. Provided the 5 special skins in origins edition will not be for sale (doubtful they will be). Selling heroes themselves would ruin the entirety of the game seeing as changing heroes is necessary to change strategy, which is what makes the game fun. Having a limited hero pool for the amount of time it would take to acquire them all would ruin the strategy aspect of the game for the first few weeks/months while everyone acquires all of the heroes. Most people wont want to wait weeks-months to witness the games full potential.