Hi Michael,
I apologize for the delay in response.
Your thought is right. Currently, we can't synchronize two stand alone forests with a single office 365 tenant.
So, I suggest you submit feedback to our product team about your suggestion. Our feedback analysis specialists will evaluate the advice you provided. So far, many features are improved based on customers’ feedback. This will help our product to be designed better. Thanks for your effort and contribution.
Regards,
Jerry Cen