Any chance you plan to integrate with Google's Config Connector? It's very similar to crossplane (but gcp specific).
I think that'd be a bit challenging because Config Connector is highly opinionated, for example, Kubernetes Namespace corresponds to GCP project. Though it might be enabled to be used as part of a Composition when we support namespaced CRs to be used as composition member.
Every config connector resource can be annotated with the project for GCP resource to be created in. Namespece to GCP project mapping is encouraged, but not enforced, you are still free to create resources in multiple projects from a single namespace as well as in a single project from multiple namespaces.
One of the best features is that you can bundle a CR to request a MySQL database and it will be satisfied with whatever config is in your cluster so that app only declares the need but not care how it’s done.
Disclaimer: I’m one of the maintainers of Crossplane.