[EDIT] HubSpot now has a feature available through SalesPro that would make this possible. It required us to use the Sales product and get Beta access to the Deals Workflow feature. Once that feature was available, I built a workflow that said:
When Deal Property ABC is known, copy value into Contact Property XYZ.
Now that the contact property has been populated, we can pull it into the email as a personalized token.
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[ORIGINAL] I am floored this feature is not available. We recently switched from using Contact Property data to Deal Property data and this forces us to lose so much of our personalization across the board in critical emails. Please add this!