I'm not the only one that whishes to sync non-local files to my iPod. I understand that Spotify can't just release all of their streaming music to even premium subscribers without negative consequences. Allowing full iPod syncing freedom would allow users to pay for one month, take all the music they desire, and then cancel their subscription with no consequences. This is piracy, and would certainly ruin the integrity and probably lead to the collapse of Spotify.
If Spotify were to allow non-local syncing, here's how it should be done:
Any non-local file synced to an iPod should have an expiration date of, say, 30 days. This way users would be forced to continue their monthly subscription in order to re-sync their playlists and keep songs active. If a user syncs 10,000 songs in one day and doesn't renew their subscription, the songs will expire and never be playable again.
The idea is simple enough, but I'm sure integrating this into song files and not counting days from the date on the iPod would take some finesse. This is where Spotify can help!
I would love to see this happen, and I don't think it's unreasonable to pay a subscription to receive full usage of the songs I stream from Spotify. Maybe this in addition to the ability to purchase songs outright would cover all the bases for Spotify. Eventually the price of renewing songs every month would catch up to itself and validate full purchase. Full purchase would simply wipe the date-stamp from synced songs.