I would love to see someone create a "marketplace for rent control rights" in housing markets currently being fucked by rent control.
The idea here would be that anyone with rent control for a certain unit would be able to put out an offer for conditions under which they would vacate the property. Once you have standing offers for all units in a building, a developer could make a bid to satisfy those rent control rights and buy the property from building owner.
People with $800 rent control in say a studio might be willing to exchange their studio apartment for a 1 bedroom in a new building within 1-mile in the regions of a city, and this new unit would come with a contract for all the same rights as rent control, but that it would be limited to that tenant and that tenant alone (it can't be "passed" on by adding people to the contract).
So lets say I'm a developer with a few properties under construction. When I see a building where all the tenants have made offers that I can meet in some way using units in my projects under construction. I crunch the numbers and make offers to each of those individuals. Once I get all the tenants to accept the offers I make, I then approach the property owner and make an offer on the property. Once I buy the property, I can then give each of those tenants a property in my other buildings and then demolish the original building and build something taller with more units. Even if I destroy the old building and build something newer with only marginally more units because of zoning laws, I would now have a new construction free of current rent control rights.
The key here is to create legal mechanisms that make rent control rights a fungible commodity that can be traded. By making rent control rights fungible, you essentially decoupled the rent control from the physical structure, you create a way for the owners of the structures to be able to use the land under that structure for its highest and best use.
Furthermore, this approach is much more amiable than Ellis Act evictions since it gives rent control renters an out that is comparable to their current situation. Even more, it gives them the opportunity to move to a larger unit in case they've outgrown their current rent control place and would like to stay in the city to raise a family (e.g. someone with a 1-bedroom can requests offers for a two bedroom place at a comparable rate relative to their current living situation).