One of the biggest benefits to having a Dual Drive is that a very large gear range can be maintained, but a short cage derailleur can still be used, perfect for a bike like the Tikit where ground clearance is small and precious.

A short cage SRAM X9 would handle your proposed 60t crankset and 11-34t cassette, it would also be a good match for the dual drive system. Medium cages may still provide you acceptable ground clearance for city riding, which would include many more options.

Capreo cassettes can also be modified if you know what you're doing and people have modified them all the way to 9-34,

As an example, I see this business called Utahtrikes is doing Capreo wheel kits, and offering them with the cassette pre built into a 9-34.

http://www.utahtrikes.com/PRODINFO-S...Wheel_Kit.html

26.3"-99.4"

That's pretty good on both ends.

Combining that custom Capreo with the 60t chainring gives you 29.8"-112.5", heh.