A sequel to Killing Floor is likely in the works, based on a glitch on Steam earlier today that swapped its stats page for a list of titles not yet announced.
As captured by NeoGAF, the list contains mostly known quantities, but there are a few surprises on there like Killing Floor 2 and Half-Minute Hero Two ostensibly making its western debut. There's also a Steam port of Battleblock Theater and an HD version of the Vita and 3DS Batman: Arkham Origins spin-off Blackgate.
Half-Minute Hero Two was released in Japan last year, but has yet to see a western release. In November publisher Marvelous AQL's producer, Esteban Salazar, told Siliconera "It's considerably more expensive to put out the sequel and we need to sell a lot more of the first game on PC to begin to justify it."
This Steam leak isn't conclusive, though, as some of the listed titles are clearly just testing grounds for larger projects. For example, there's a listing called "Counter Strike: Global Offensive Beta Dev PS3". As such, it's not 100 per cent clear if the games listed here are actually going to see the light of day, but it's a promising sign at any rate.
We've reached out to a handful of developers and publishers attached to the leaked titles to try to confirm the report, but we've yet to come up with any official confirmation.