"As a user of Stripe Subscriptions, you will get all the functionality of Stripe Billing's starter plan with no change in price. You can continue using it free of charge on your existing Stripe pricing, even beyond the $1M free threshold. This will be automatically applied to your account. Contact support@stripe.come with any pricing questions"
As far as I can see, the Billing Starter plan has not changed and still applies. Not only that, it claims we get "all the functionality of Stripe Billing.." when this hasn't been the case for a few months. New features have been gated recently, ie. the new customer portal.
You have every right to change your pricing how you see fit. However, if this message was worded as it being a grace period, we would have taken steps two years ago to consider other tools or building something in-house.