Calm down, they were all rough numbers, but just showing possibilities of where to take out a good amount of weight. Here are some actual examples.
If you take it both 15-20kg front seats and replaced them with fixed position 6-8kg ultra light carbon Recaro QRT-C
A 4kg LiPo battery vs a 18-20kg lead acid
Pretty sure I can cut 10kg off the front and rear beam RS4 beams combined.
A Volk CE28N (or lighter) with a lighter tire vs the heavy stock wheels and tires, pretty sure between a set of 4 you'll save 2-4kg each. That's rotational mass so even better.
4 Stock rotors vs Project Mu SCR-Pro 2 piece front and rear, pretty sure they save close to if not more than 1kg each, so all together roughly 5-7kg. And again that's rotational mass so even better.
HICAS rack weight I guessed on, but still heavier than a Midori Seibi or Cusco HICAS delete.
Aluminum or chromoly links will weigh less than the factory stamped steel links and cast front lower arms. Depending on brand, bushing type, and other variables I figured between 8 arms and links you could squeak out 5kg but possibly a tad optimistic.
Factory prop shaft 13.7kg vs carbon shaft 6kg (sorry, not quite my estimated numbers)
Stock suspension roughly 7kg per corner vs my Flag-L at 5kg, so 8kg for the set of 4.
Billet RB block is quoted as 46kg vs stock at 70kg. 34kg savings. Sorry a bit optimistic on this one also but cut down the crank counter weights and run some Ti rods and you'll lose the other 4kg 😄
I forgot these:
Full Titanium exhaust vs stock steel piping
Titanium or aluminum IC piping vs stock.
300M CV shafts (gun drilled of course)
Ceramic CV balls
Take out the floor mats
Go on a diet
Now I'm not saying any of this is budget friendly (or even close) but it's all possible without driving around in an stripped bare empty tin can.