Below is a collection of tag-values I have started using and would like to present to a broader audience. Because all of these are new (or adopted) values for existing keys, I am wondering if formal proposals are needed, or if documentation on the wiki will suffice.
Analogous to footway=link, cycleway=link marks bits of cycleway that are needed to connect cycling paths to the rest of the road network, but which are not represented by a direct physical presence (e.g., lines, barriers, or signs). Explicitly marking these 'virtual' bits of cycleway with cycleway=link lets other mappers know the function of these ways, and provides renderers with the possibility to de-emphasize or otherwise render these in a slightly different manner.
The cycleways on both sides of the road going East from the crossroad (shown in purple) are separated from the main road by a low barrier, and mapped separately. At the crossroads, these parallel cycleways end, and cyclists continue their way on the residential roads going North, West, and South. The red ways in this JOSM screenshot are typical examples of bits of cycleway linkage, and are tagged with cycleway=link. They connect the cycleways to the residential roads, but no markings appear on the road surface. Conversely, the purple parallel cycleways are explicitly marked by a barrier separating them from the main road, traffic signs for cycleways, and a reddish surface.