IIUC it already does this. Many of the libraries Pulumi exposes are not specific to any cloud platform. Examples:
- Docker: https://www.pulumi.com/docs/reference/pkg/docker/
- Postgresql: https://www.pulumi.com/docs/intro/cloud-providers/postgresql...
- Keycloak: https://www.pulumi.com/docs/reference/pkg/keycloak/