If the changes are anything more than data driven in nature (ie. core engine code changes) then an expansion pack likely isn't a feasible option. It all comes down to their base architecture and the kind of extensibility that it allows for.
Not that the angry masses will care about the rationale behind it. They're fueled by the Righteousness of Intarwebz Justice!
Not that the angry masses will care about the rationale behind it. They're fueled by the Righteousness of Intarwebz Justice!