Block Visibility Needs to Follow Ownership Dates

We had one of our properties change ownership recently. We were shocked to discover that the new owners were able to see all the blocks that property has ever had in its history! If it's going to be forever before portals have date visibility controls, at least make it so visibility follows their ownership dates!

In the meantime, the best workaround I've been able to come up with is to create a bunch of custom booking sources. Instead of ever using blocks, everything is recorded in OR as a booking, whether it really is or not. Then relevant booking source filters on all reports and triggers keep them from showing up where they're not needed.