So what's it like? Well, it uses the same mid-mounted 1.5-litre three-cylinder petrol engine as the Coupe has always done, putting out the same 231hp and 236lb ft of torque. Overall performance is up, however, to 374hp and 420lb ft, thanks to a 12hp bump to the front mounted electric motor. This should make the i8 Roadster good for a 0-62mph sprint time of 4.6 seconds (0.2 seconds slower than the Coupe) and a limited top speed of 155mph.
As with any convertible, a lot of attention has inevitably been focused on the roof. The newly-developed fabric structure opens in just 15 seconds and stows beneath a panel integrated into the buttresses behind the passenger cabin. Unfortunately that means sacrificing the Coupe's 570GT-style luggage deck - but fear not, as BMW will sell you custom bags that fit into compartments totalling 92-litres worth of stowage space behind the seats. Of which there are now only two; the Roadster also losing the four person capacity of the Coupe.
Inside, the updated dashboard from the facelifted Coupe makes its way into the Roadster too, with the latest version of BMW's iDrive system in tow. There are newly designed seats too, and buyers have the option of a head-up display as well as a range of carbon fibre and ceramic trim options.
So it's slower, less practical, and probably more expensive than the Coupe, but that's kind of missing the point, isn't it? The long-awaited convertible will go on sale early next year alongside the facelifted version of its Coupe forebear - but if you can't wait until then there are plenty of very attractively priced alternatives in the classifieds...