fmattheus, Dahon Mu has 103cm wheelbase which is quite long. Actually all Dahons have the same (its called Biologic II geometry). You can easily put an ahead stem on the telescoping part of Dahon handlepost (with an 1-1/8" to 1" reducer). Strong enough to hold a drop bar or a bullhorn (bullhorn can be mounted such that fold isn't compromised). BTW, Dahons can accept caliper brakes if you install 451mm wheels.
Mu XL does come with Nexus hub. Mu P24 comes with dual drive.
Generally, to mount a dual chainring you'll need to find a front dereilleur to fit the bigger seatpost diameter.
Regarding heel strike you have two options. Either use the low rack and pack things on top. Or use a higher touring rack (slightly bigger package when folded) with standard geometry. There are also front racks for side panniers available.