MK8 - Konno (prod.) & Yabuki (dir.) E3 itw
An intersting interview with Konno and Yabuki during E3 published by the French website Gamekult. Sorry if old.

Direct link, in French:

Google translation link - it's ok quality I think:

My highlights:

- MK8 development began just more than a year ago.
- No others studio involved, 100% EAD Kyoto.
- About the Gamepad use: "Our priority is to provide the remote display on the GamePad only. We have other ideas, but that's all we can tell you for now."
- Why no F-Zero instead ?: "H. Konno: It has always been a Mario Kart per console, so we wanted to get a new one to have more people interested by our new system. But I also hope that there will be an F-Zero.

- About tracks size: "In Mario Kart 8 tracks have also been narrowed compared to Mario Kart Wii and reflects more the size of the road. "
- About customization: " Like Mario Kart 7 (but) with a little more choice"
- No editor even if they talk about it.
- About a Double Dash mode using the Gamepad: "H. Konno: For Mario Kart Wii, 7 and 8, we decided not to use it. But this is a request that is often heard, so maybe we can meet this desire.