It's a network effect thing - if enough people used an OSM client and opted into sharing anonymized location data, you might be able to get somewhere with it.
In practice, I think it'd have the same problem as the core map data - surprisingly good data in places with a lot of adopters, and nothing at all in places without.
That said, though, the traffic data is pretty secondary - a good, open routing engine would be lovely to have, and will slowly become more relevant as the map expand and fills out.
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I suppose Google also has the user-collected data that can tell you which routes are going to be busy. Almost impossible for OSM to replicate that.
It would be hard, yeah.
It's a network effect thing - if enough people used an OSM client and opted into sharing anonymized location data, you might be able to get somewhere with it.
In practice, I think it'd have the same problem as the core map data - surprisingly good data in places with a lot of adopters, and nothing at all in places without.
That said, though, the traffic data is pretty secondary - a good, open routing engine would be lovely to have, and will slowly become more relevant as the map expand and fills out.