Ideally what I would love to see eventually is four new UK cities. Specifically two at the most northern parts of Scotland on the east and west sides. Not sure what the roads are like that far north, but I imagine they could make for some good driving.
Then maybe one or two in Wales Central and/or in the North West.
I have many little ideas I would love to include. Shame I can't map mod.
Gotta say, completed a run from Brest to Southampton last night, there's some lovely new roads up there and I love the motorway/roundabout style interchange.