Found 30th May 2017
UPDATE: The Humble Bundle Store have joined in the pre-order fun as well at the same price, which means if you're a monthly subscriber you'll get an additional 10% off.
Pre-orders have gone live over on Steam, with the usual 10% discount thrown in for those who want to secure an early copy. I really hope this ends up being the Sonic game we've been waiting for, as previews have been generally optimistic so far saying it's the old-school-like experience we fondly remember.
Seriously, I'm crossing everything.