[waterfoul]

I have plans to implement radio, but sadly there are two roadblocks on the way:

• Spotify recently removed radio support from their API, so in order to implement this feature we'll have to look somewhere else.
  
• A possible way could be to use Echo Nest, but sadly the call rate limit is too low for non commercial uses (great for a single client, but unsuitable for many clients making simultaneous requests).
  

I actually disagree with your statement of Echo Nest as you can use local caching of the playlist decisions and every 5 songs do your dynamic/steer and dynamic/feedback calls (would only need one of each) then run dynamic/next and get 5 songs This would make the playlist less dynamic but would effectively let 100 users simultaneously use it (max 3 calls every 15 mins assuming 4 mins/song). You could also use the X-RateLimit-Limit/X-RateLimit-Remaining values to slow or speed up the api calls (I would say 10% use would be update every song, 50% use would be update every 5). It also looks like the echonest guys would be willing to raise this for cheap/free. I would personally be willing to help develop this type of feature and would probably be willing to throw a little of money in the pot if we need it.