...it would be even more useful if it had a swivel so that it could be used on a handlebar or other horizontal bar...
Andre, might it be possible to "stack" one of these on your SKS mount to achieve a swiveled position?http://www.topeak.com/products/Bottle-Cages/X-15Adapter
Perhaps one of these would work on the 'bars; I see it can be oriented either vertically or horizontally, depending on need.http://www.topeak.com/products/Bottle-Cages/cagemount
Topeak's innovative solutions are very helpful for those who need to carry water in nonstandard locations or for those whose bikes lack mounts where needed.
For obvious reasons I'm not too keen on in-tube cabling on steel bikes...Heartily agreed
, though I managed to get it working on my tandem, which has all-internal cabling for the whole run to both derailleurs. Did it by weather sealing the top entry and leaving the bottom open to drain/air. Really no alternative, and it has worked well and completely rust-free internally so far after 23 years (I can take out the front eccentric and rear BB and see any problems as they develop). No rattles and smooth shifting, thanks to the full-run low-friction liner I installed. Internal cable runs are generally best avoided on steel bikes.