Often I wish to take friends along on fun drives, and 2 seats just aren't enough. Dave since you mentioned multiple derivatives of the 818 platform, how about a Lotus Evora type "4-seater"
With the flat boxer motor, maybe the occupants can sit on the gas tank, or engine.
Or how about a McLaren F1 type 3-seater setup?
It may require stretching the wheelbase, or not, you guys are the experts.