I assume you're talking about the M3CSL?
That is a stripped out, tuned version of the M3 coupe, but it also features different materials for some of its body panels (carbon fibre roof for example) to achieve a lower weight.
This is an interesting exampe, because by buiding this car BMW has been able to undercut the pricing of its rivals, as this is pitched against GT3 porsche's and even the 360 Challenge Stradale, not just the M3 brigade.
VW wouldn't consider messing with the recipe for the current Golf GTi, so a stripped out version would have to be sold side-by-side to the standard car, as you suggested.
If less (equipment and weight) means more (money, as it does in the case of the BMW, its ?10k more than a standard M3) then what would the rivals to this stripped out GTi be?
The performance gains of the weight loss wouldn't be sufficient to move it into a different 'league' of cars, so it would be an (admittedly more capable) but horrendously expensive alternative to the rest of the hot hatches available.
Only if it were cheaper would it work, and the current fashion for manufacturers is to add more cost when stripping weight.
I'd have one though