Looking for a Unicorn (bike) - High performance, lightweight, low step
R&E Cycles (aka Rodriguez) in Seattle should be able to custom-build what you're looking for. They have a step-thru option for their frames. They can do custom geometry. They can do traditional geared derailleur or Rohloff. Can add S&S Couplers.
https://www.rodbikes.com/profiles/pr...php?tag=single