According to folk on Facebook, Motoring News have an article saying Donington made a loss on the WTCC this year and are talking to Knockhill about transferring the date to them! Until now, I'd always just assumed there'd never be any point even thinking about anything international visiting, but it does actually make some sense; crowds are unlikely to be much bigger than BTCC ones (so roads etc should cope alright), the track is getting upgraded more and more over time and is apparently above the required FIA standard for touring car races.
I'm a little surprised it wouldn't just go to Silverstone/Brands or maybe Rockingham, but I guess if they've already got plans for those dates or just aren't interested, why not Knockhill? Fascinating idea, I've no idea how good the chances are of it really happening but I would LOVE to see it. (Even if it does mean I can't go in the end; Donington is in easy reach of me, Knockhill involves rather careful holiday planning! )