I am currently building up a classic touring bike in AL frame, with maybe a carbon fork. It is hard to see how much weight one can save, over that. With carbon the cost would be around 350 all in. It would still be a mule for 4 bag travel as required. And one doesn't have to do foolish things with no purpose.
The BF calls me too. Unfortunately AC has just cut back on the bag size, and I don't think any bike will fit in the new size, not for 58 CM, but I haven't actually looked into it with care.