Winter can been seen as off-season for bicycle things. This is not completely true, people are defining (or specsing) new complete bicycles, frames and parts for their new ideas of their cyclist career. Some propel heads and folio helmets has totally new approaches to problems in question.
In tandem, primary chain tension might be problem if you do not have eccentric bottom bracket. This solution was done with two extra chain wheels floating freely between lower and upper chain. This fixed gear tandem was build in Pyöräpaja and it was seen in Yksivaihde.net x-mas party.
Helsinki city is taking good care of the normal roads in winter but roads for bicicles are in so bad shape, so I started to ride fat bike in last winter. Second winter, with hub motor in front, 30km daily commuting ride is pure bliss for the lazy bastard. Cargo sledge pulled to the same party by eMulkul.