Hi Thomas!
Two of my friends likely bought the same frame. In each case, chain tensioning is accomplished with sliding Rohloff OEM dropouts rather than an eccentric bottom bracket.
In each case, they started with a derailleur drivetrain and converted to Rohloff as funds allowed.
One plugged the threaded hole with a bolt, though he uses a front mudguard and long mudflap. He figures on removing the bolt periodically to check for and drain any water that has entered. Thanks to a heavily greased seat tube/seatpost and a bit of vinyl electrical tape over the frame vent holes, there has been no water entry from those points. However, a small quantity of water enteted through access points for the internal dynamo light wiring, and the maker confirmed this on inspection. It caused a small amount of surface rust/discoloration inside the lower down tube and in the BB shell. He was advised to periodically remove the bolt to drain the area and allow air circulation and to also spray a water-displacing lubricant through the hole. He lives inland away from salt air but with high humidity and the bike sits outside while he works and comes into a heated room at home.
The Second friend eschews mudguards, rides in all weather, and left his BB cable-clip/guide mounting bolt out. He found the front tire tends to throw a surprising amount of water through the open hole, whose threads have now rusted to the point where a bolt won't thread in cleanly anymore. His philosophy is that any water thrown in can drain out again and he remains undisturbed. He lives in Rotterdam and works in Hook of Holland, a coastal clime with salt air. Having seen the flaking orange rust inside his BB and lower downtube, I would be concerned it may be well on its way to a more advanced state of decay.
Two data points at polar extremes. Hope this helps.
Best,
Dan.
