Game Maker studio exports to Linux so we're very hopeful for a Linux version. However, due to the complicated nature of the game's multiplayer and Steam integration, it's currently a bit risky to promise a fully working Linux version.
We'll let you know as soon as we find out anything.
Just add multiples of £8 to any pledge above Tier 1 and we'll confirm this in a backer survey if we're funded. As per Kickstarter rules, the maximum number of copies you're allowed to add per account is 8.