The .35 case already has a short neck and not that much body taper.
First off I agree that if the 35 Rem were a great candidate for improving it would have been done (widely). At the same time I've heard the body taper comment a number of times before. I never did the math but that always struck me odd as when looking at a 35 Rem case it doesn't look too straight-walled to my eye. Anyhow tonight I got out a couple of my reloading manuals for reference drawings and did the math: the 35 Rem case body has approx 40%
more taper than the 30-30 which is probably the all time favorite improved case (i think).
No, it does not have a lot of neck for moving the shoulder forward (which is a big factor in the 30-30) although I always thought the reasons for improving in these break-open actions was (1) reduced backthrust and (2) case life more so than the increase in case capacity so I'll relegate that to third place.
Oh, well... I'm happy with my 35 rimmed as is. Up to this point I've resisted the urge to modify it and just spent the energy and $$$ adding different barrels.