Hmm, I don't know. I can think of a couple reasons a fellow might want one of these. Cost/benefit is definitely subjective, but even if your goal was simply to match the RUM in a 3.34" round, you may get better accuracy due to the shorter burn column (I have no real knowledge about that; it's definitely been tossed around as one reason the 308 can be more accurate than the '06), and if you did have a full-length action, you could seat some pretty heavy VLD's out to 3.6" and end up with more powder than the RUM with equal COL.
Give it a 30" bbl and you might find all that powder actually does make a difference. I bet you'd see 100 fps difference with a 240 SMK against the RUM case at 3.6".
Sure, you can shoot 1k with a 308. But you don't have to. This would definitely be a specialized cartridge, in a specialized firearm.
Another thing to check out would be the ballistics of the 30-378. You better have 300g bullets and a pole the size of my nose to make that thing hum.