Either way, building an extreme light weight mountain rifle or a something with better range capability right up to a full blown tactical rig.... nothing changes, you save just as much weight with either build if you go carbon vs wood/alu.
The extreme light mountain rifle often had flaws, I had built myself sporter barrelled rifles with 20" barrel 20OZ carbon stock and also had a 32mm scope but especially when going into the hills the shots are longer and this type of set up is not the best. Great for walking.. not so great for the longer shot. For certain applications it was perfect just not an allrounder. Recon it depends a lot on how, when and where you shoot. When I go into our hills now I take a lightweight tactical rifle, go on my own and pace myself. Coming back with the meat of a deer in the Rucksack is the bigger issue. Then again we mostly only do half day stints into the low'ish hills.
edi