I recently tagged the Stadt Zürich Velovorzugsrouten (e.g. https://www.openstreetmap.org/relation/18164970) for similar reasons :)

I think the state tag on OSM has a slightly different meaning to what the canton's dataset might say: something in the default state on OSM is supposed to be findable on the ground. So for a route, that means you should be able to find _some_ route wayfinding signs/paint/etc. But at least in some of these cases, there really is no bicycle wayfinding at all, as far as I can recall from my last ride through.

Although one shouldn't map for the renderer, for what it's worth both CyclOSM and OpenCycleMap render state=proposed cycle routes, just with dashed rendering. Which IMO is appropriate: a user might be rudely surprised if they see a route on the map, assume they can follow it, and then find it not signed in real life.

There is one annoying thing, which is routes can only have one state value for the whole route. You can't mark just the sections that are not signed, for example. For the VVR I decided to err on the side of caution and tag them as state=proposed if they had significant portions not signed. The lcn=yes tagging on ways is in this respect more flexible.