For costs, it allows an unlimited number of users since it is priced by aggregate capacity (see Power BI Premium calculator). Users who need to create content in Power BI will still require a $10/month Power BI Pro seat, but there is no per-seat charge for consumption.
For scale, it runs on dedicated hardware giving capacity exclusively allocated to an organization for increased performance (no noisy neighbors). Organizations can choose to apply their dedicated capacity broadly, or allocate it to assigned workspaces based on the number of users, workload needs or other factors—and scale up or down as requirements change.
They’re throttling down Power BI Free, making it really just for personal use, but I think the Premium tier will help with pricing for adoption.