I want to be able to have a load balancer between App Platform apps, and potentially even any IP address (including non-DigitalOcean managed) or domain name.

The purpose for this in my case is to make use of the Global Load Balancer, across the same App Platform apps in different regions, as well as in other cloud services by IP or domain name - potentially as multi-cloud redundancy, or partial migration of an application to DigitalOcean.