I don't think the buying public really think about power to weight ratios. I just don't think it would sell.
As a former biker, I can tell you about that - I can tell you that a 188kg Yamaha R1 with 128bhp is a ratio that nobody who has only driven cars can possibly understand. You know that bit in star wars where the stars all blur to lines.... its like that lol!
You could make a GTI+ I guess by:
Using different materials for the bonnet and roof - maybe aluminium or carbon fibre?
Lighter forged wheels, maybe 17's, narrower tyres too
Lighter brake calipers and discs
Not sure that would make enough difference vs the money spent. Maybe shed 100kg like that? Cost maybe another 2k?
Removing the 2 doors and making it 3 door drops a fair bit of weight.
Then you could start to do things that nobody would want as a daily driver:
Remove AC
Remove all sound deadening
Remove carpets
Remove interior trim panels
Remove dash
Remove back seats
Replace front seats with lighter recaros
After that, its horrible to live in but probably what, 500kg lighter?
The actual TCR touring car is only 100kg less in weight than the road going "TCR" because after removing all of the nice things it has a rollcage and extra body panels.
Bizarre eh?