Aside from oversubscription only a fraction of any customer's traffic will traverse the IX. The ratio will depend on who Starlink is peering with on the SIX (not necessarily everyone) and the traffic flows to/from those ASN's.

That said there are some very significant content peers present on the SIX: Akamai, Amazon, Apple, Edgecast, Facebook, Google, Microsoft, Valve, among others. Hurricane Electric is also there and has an open peering policy despite being a very large ISP with a significant percentage of Internet routes and traffic.