Thanks for reaching out to us.
Yes, it's true that you can't add IF to the SM for the moment. Our SM team is working on adding Integration Fields to the SliceMachine.
In the meantime, there is a workaround that you can use. You can add the Integration Field inside the
model.json file of a Slice. This will allow you to push your Slice with Integration Field to the Prismic UI.
The drawback of this workaround is that this field will not be usable in the SliceMachine UI (it won't be editable, will appear as "Field type "IntegrationFields" not supported", and it won't be populated with dummy data for preview and screenshots).
When we release SliceMachine support for Integration Fields, we'll communicate it publicly on our progress page: What's new - Prismic
Let me know if you have any questions about this.