It turns out there's no way to sync files between a phone, and a desktop without wifi. That, I can imagine, it limiting for a lot of people. It is for me at least. I have a gaming rig. Dual ethernet, but no wifi. I have no need for it. I shouldn't need to be forced to buy an external antenna, just to sync my local files from my computer to my phone.
Your Idea has been submitted a while ago, and unfortunately hasn't gathered enough votes (100 per year) to keep it active in the Exchange. Be sure to know that this does not mean that your Idea has been declined by Spotify.
If you still feel strongly about your suggestion, we encourage you to develop your Idea and post it again, with a link to the original one, to give it a chance to gain more votes.
For more info on how the Ideas Board works, click here. :)