3 things you need –
1) Some way of transferring torque to the frame. The Rohloff ‘OEM’ dropout is the most elegant and is built to handle the stress. A ‘speedbone’ which attaches to the brake bosses is the other. Rarely causes issues but can.
2) A way to tension the chain. Either
– sliding dropouts and a pivot around the BB so no change in chain length. Restricts you to a very small number of frames and compromises suspension design
– A chain tensioner (and some sort of chainguide at the front). Rohloff’s parts work well and last a long time. Very rarely dump the chain with them – the only issue is clearance between the guide and cranks with some crank/chainring combinations.
3) some way to route the cables. For light shifting you want as smooth a route as possible – under the bb and under the chainstay normally works best. Cable ties/stick on guides will work but for elegance best built with the frame.
Nicolai, of course, offer OEM dropouts and Rohloff cable routing as no cost options on all of our frames.