LightSail as a managed service for hosting of 1000 WordPress sites?

Lightsail is generally for smaller projects and has limited scaling capabilities (it now has a simplified load balancer but no autoscaling). Personally a better option is to use ElasticBeanstalk as it give you the advantage of not having to fully manage the underlying ec2 infrastructure but comes with Autoscaling and ALB access. It also allows for blue green deployment and detailed monitoring and scaling features. If the customer is planning to host 1000s of wordpress sites then they will want to have access to all the monitoring/scaling automation that are out there.

Here is the tutorials on hosting wordpress on elastic beanstalk:

• https://docs.aws.amazon.com/elasticbeanstalk/latest/dg/php-hawordpress-tutorial.html
• https://aws.amazon.com/getting-started/hands-on/build-wordpress-website/