Among many the bad terms disclosed in the article, IMO this is probably the worst - basically, this right is a license to cash out and torpedo the company within 3 months (just the right amount of time to see how the market reacts to Spotify's first earnings call as a public company..), leaving the other investors (and employee common stock holders!) with greatly devalued stock.
Of course they have a disincentive not to do this: if they did start to sell after 90 days, the stock would start plummeting before they could sell all shares, so the last shares that TPG/Dragoneer sell would be worth much less than the first bucket of shares, but if they do sell it means that things are very, very bad and they'd rather cut their (20% discounted...) losses, and will be much, much better off than the other investors and employees 3 months later.
Edit: The more I think about it, doing nothing would be most optimal. Doing nothing is so much more cost effective when you know it's a inevitable decline.
Stock compensation is a lot less competitive here due to it being taxed as normal income for the most part. Not to mention salaries being a lot lower in general than USA or some other parts of Europe.
Basically: they're kinda fucked if it goes south.
I look forward to the inevitable pump and dump around IPO time.