The State of the Code has been updated with word on the restrictions on purchasing a mansion, or rather the lack of.
The Mansions released in December and January did not have the appropriate Monarch and Rank 6 purchase restrictions that Mansions are supposed to have. These will be fixed in February. However, when maintenance is due, the Mansion automatically checks for Monarch and Rank status of the owner, and the owner loses the Mansion if these requirements are not met. If you purchased a Mansion without being a Monarch and at least Rank 6, and you are not a Monarch and at least Rank 6 when the Mansion's maintenance period next becomes due, then you will lose that Mansion.