Most teams start with a car that is around the weight, about plus minus 10kg or so. The largest cut in weight in the past 6 or so years has been the HRT F110 in 2010, it was 20kg overweight, but by Japan it was 60kg under with a change in materials under the skin. It shed 80kg over the year, and the largest handling improvement setup wise was the ballast as thats how it was faster than the VR-01 that season and just a few tenths behind the T127.
Id recon that the change in power unit would be a percentage of the 30Kg if that figure is true, id recon that up to 7kg of that will be in the latest carbon fibre layup techniques and materials in the chassis, and integration of the side impact panels into the chassis and not being mounted crudely.
I think this chassis will see one major upgrade, but under the skin, if they manage to reduce the ballast free weight by a few more kilos her and there, they can extrapolate more time in ballast position and tuning. And if they get a handle on the setup quick and with enough quality aero upgrades, i think this chassis could easily be a midfield beater. If they get their new thumb nose and new front wing for Australia as i have read, it will be a promising start. They have the technical staff to extract the best out of this car out of the car, lets hope the drivers can do so in the car as well.
Im looking forward to see how it develops as the season goes on.