Hi @Kaz,
Probably, I don’t get the entire idea, but any expansion licenses for Emlid Flow won’t affect Caster opportunities anyhow. To become a public NTRIP service, it should have a corresponding infrastructure: base stations, servers, and so on. We develop it as an NTRIP Caster, not the service.
For building your own NTRIP service, we suggest Emlid Caster Pro. It has two tiers that allow connecting up to 20 and 50 bases, and up to 1000 rovers. You can start a one-month free trial if you want to test it, just leave an inquiry below Caster Pro page.
By the way, you can read our Support tip regarding this matter. It may also shed some light on the topic.