This is exactly right!
I think that 5M is a high number (at least with the current number of satellites and their architecture), specially if they do not apply data caps.
I would say that 1M customers in the US is a more reasonable figure. If they hit these number, I expect the performance to degrade significantly.
In the US their plans are to be able to support something like 5 million customers. That's less than 5% of the number of customers Comcast has.
It really is by design meant for people in areas that do not have terrestrial broadband.