There is just one problem that also followed L4D1. As soon as they release sequel, player count of old version will severely drop. And that isn't good for any game based on online play (mostly).
The same reason why Killing Floor devs are hesitating to change the platform even though they'll just have to because they are already hitting the Unreal Engine 2.x limits... but they don't want to cruble the userbase.
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