Like the recent Kaby Lake XPS 13 9360 update to the Skylake XPS 13 9350, the Precision 5520 will likely be the minor Kaby Lake update to the existing Precision 5510 Skylake SKUs.
http://www.notebookcheck.net/Dell-leaks-Precision-5000-series-with-i5-7300HQ-i5-7440HQ-and-i7-7700HQ-options.189516.0.html