The Sitecore team has identified an issue related to the "Location" list selection box in the Region tab for the Azure Marketplace deployment interface. Sitecore Engineers are aware and working to fix the issue as soon as possible.
Completed:
Microsoft corrected the underlying issue; the "Locations" list now populates as expected in the Sitecore Azure Marketplace.
In Progress: Sitecore Engineers are working to resolve this issue.
Identified: Azure Marketplace deployments cannot be completed.