Heres an interesting articlle on the follow up to the Lancia Delta S4, the ECV1/2.
http://www.carsfromitaly.com/lancia/index.html
I also understand Austin Rover had a Group S version of the Metro 6R4 on the go which according to Cars & Car Conversions magazine had a 'radical' new engine.
I would have thought Ford would have had there Group S car on the drawing board as the RS200 EVO was already completed by the time Group B was banned.
And of course Peugeot would have had a car planned.
Heres the MR2:-
BTW, wasn't Group S menat to be limited to 300BHP. Yet with ever improving turbo technology they would have been putting out 500BHP+ even with the small (was it 1.3L max) turbo engines they were allowed.