Stargazer - Glad you liked the photos of my bike. I just wanted to do something different than all the other "race" Swifts you see here. I wanted something unique yet very versatile. Sort of like an Audi Avant Quattro. It is amazing how different it looks compared to the other Swifts but with the exact same type frame.
As of front chainrings, I am running a 53/39 front double on my Swift so it is definitely doable. You can run a rear derailleur if you want or go and internal 8spd hub like I did or even a DD setup if you prefer. The bike lends itself to many different cofigurations.
I personally don't see the need for the DD setup unless you need and extreme range of gearing. I like the single cog on the rear because it is easier to pack in a suitcase, less gunk on the rear and nothing really hanging down that can get busted off to speak. When I had a big sprocked on the back my derailleur on the back hung down REALLY low and I caught a lot of grass with it do to the 20" wheels.
I find it is quite easy to carry on my shoulder like you mentioned. I sling it over my shoulder (when it isn't muddy or wet) and it's pretty easy to balance. My fully kitted Swift weighs less than a Speed TR and mine has fenders, rack and internal hub.
Either bike is a nice piece but when I decided on a new platform for my custom bike, I went with a Swift. I still have a few things left to do but it is so pleasant to ride that every spare second I am out cruising on it. Tonight I rode about 10 miles with my kids even though there was a lot of snow and ice in some areas. If you do go with a Swift, I HIGHLY recommend the going with the Deore XT brakes. These things are really nice and progressive and worked pretty well even when my rims were wet.
If you have any questions that require a lot of detail about my Swift, feel free to email me directly or send a PM.