100Gbps today is like 300 customers. Hmmmmmm
It gets better as you with faster connections and more users. At 100Mbps you can roughly do 20:1 over subscription, bump that to 1Gbps and 50:1 generally works fine. StarLink is aiming for roughly 50-100Mbps connections so this likely represents around 20,000 to 40,000 customers per 100Gbps link.
“SpaceX - Starlink (AS14593) has added 2x100G bringing their capacity to a total of 2x2x100G. They are connected to the route servers.” In other words they hit 40,000 to 80,000 customers and are preparing for another 40,000 to 80,000.
Meaning that ISP B will need to upgrade its ix port at a much later date relative to subscriber count, but its PNIs and cross connects are opaque and hard to know about from a public/external third party perspective.
One station feeds about one state on average, and I doubt they're feeding everything through that one connection.
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.
I got curious and checked the local IX (smaller EU country), one of the largest ISPs has 4x100G connections, but their combined maximum ingress+egress almost never goes beyond 100G.
Dedicated gigabit bandwidth is still in the thousands of euros monthly, or in the hundreds in optimal situation (if you're already in a well-connected colo).