I ran a variation of something like this myself for years. Eventually, the site was routinely being used for spam-style (e.g., a link to some illegal data, or some advertisement to embed somewhere, etc.) links. And when I took the site down, my users asked me for help to transition away from this service that they were uniquely relying on. It was a mess. See goo.gl. I wonder how you prevent your service from being used inappropriately and how you handle the eventual costs