Whoever tags bicycle=no based on practicality evidently sees it as self-explanatory, just as whoever tags bicycle=no based on a sign or marking sees it as self-explanatory. But as we saw with highway=footway oneway=yes, signs are also very good at producing disagreement. As a starting point, there should still be a way to say, simply, yes or no. Clarification is good, but we won’t get there by assuming that an unqualified access tag always refers to legal permission or prohibition. If nothing else, there’s a large body of existing homogeneous tagging that we’d need to reevaluate – not that it’s actually causing routers to do the wrong thing in general.
(This last point is going to raise heckling from some in this thread, but I stand by it. If the situation were as dire some assume, OSM would never have been taken seriously as a navigable map anywhere. Now the challenge is to get OSM to this level of usability in the rest of the world, which may indeed require evolving the tagging scheme.)
What I’m getting at is that you need to put the cart before the horse (and maybe pick your battles too). We’re talking about some of the oldest and most common keys in OSM. This practice has been around longer than you or me. Craft a compelling alternative before critiquing the boat=no on an obviously unnavigable urban stream as a violation of a grand unified theory.