theoretically... You could do even better.
the lightest mass produced disc brake bikes out there weigh a bit under 6kg. Scott addict RC, Canyon Ultimate CF Evo Disc 10.0 LTD, s-works aethos, all in the 5.8 to 5.95 kg range. it’s safe to say that if there was some easy way to go way under that on a 2x road bike with disc brakes, someone would have. There are 4.x kg bikes out there but often single speed with all kinds of crazy bits and pieces.
so let’s start with 5.8. the tq hpr40 replaces the bottom bracket, which weighs 65 grams, and the di2 battery can go also, another 52 grams saved, so we’re at 5.68 if we start with a $13,000 build and remove a few redundant items. now we need to add the hpr 40 motor 1,170g and battery is 1,460g. 2.63kg, bringing the total to 8.11kg
a 17.86lb e-bike. this is lighter than most inexpensive non-electric road bikes - but of course we started with a five figure bike. can’t wait for the hpr40 to come to a wider range of bikes and in the USA. I think it’s likely the frames for these bikes will end up a bit heavier than the 600g ultra light ones, which may be where the 8.5 came from. still, low 18lb…