Originally Posted by
Kathranis
They're using 1.12 as their foundation, as it's the most complete version of Classic. From there will they systematically correct inconsistencies between the game version and the modern back-end architecture so that it incorporates modern stability, security, and likely login and battle.net integration.
From there they can tailor the game as the community and developers see fit. I fully expect it to not be completely identical to 1.12, as there may be some perculiar gameplay/stat/tuning outliers that would benefit from additional tuning. Take Warcraft III, for example, which has gotten occasional minor balance changes over the years for the sake of the game's longterm health.
More importantly, I fully expect them to provide Progression Servers. Which means that while they may use 1.12 (or "1.12+ / 1.13") as the baseline game version, they'll have the option to selectively peel away content and features and then gradually roll them out over time, perhaps on a set timeline or based on community voting and feedback. So for example they may launch Classic with final systems and gameplay balance, but unlock battlegrounds, dungeons, and raids following a similar timeline to the original patch cycle.