I'm sure in hindsight they would have named the Roadster the +6. Then the PlusFour would be the natural successor to the +4, and the PlusSix from the +6.

That would also leave a gap for a +8 successor if ever wanted, and keep a nice heritage lineage.

Personally I never liked the name 'Roadster' - it smacked of something Toyota would use to allude to being American.

1972 4/4 4 seater, 1981 MGB GT
1984 Harley Davidson Electra Glide, 1990 Kawasaki ZX10