How to Handle 1,000's of SSL Certificates

Our platform is a multi-tenant content management system with thousands of customers. They all have their own domains and require SSL Certificates. We increased our quota limits to 100 certificates per ALB and 50 entries per certificate. This means we can get 5,000 entries or 2,500 domains (since we need 2 entries per domain - domain + wildcard for www). This is great, but we're expecting to onboard 10,000, 20,000, maybe 50,000+ new customers/domains over the next 6-12 months. What is the best solution for handling this? We could add a new ALB every time we max out our SSL limits, but is there a better solution? Thanks!