I'm a big proponent of Land Value Tax. In theory it is one of the healthiest forms of taxation since supply is fixed. It encourages efficient use of land and discourages owners from squatting on undeveloped land just to reap value from its location. https://en.wikipedia.org/wiki/Land_value_tax
I’ve heard economists champion the idea, but I’ve heard little talk about what the tradeoffs are. What are the downsides?
If you don't allow deferment of the tax, pensioners might have to move unwillingly (low income that may not cover the tax). Most proposals allow deferment for retirees until sale of the property, though, so it's kinda a non-issue.
In general, if your circumstances change unexpectedly then you might be unable to pay the tax and thus lose ownership of your property. This already is the case for renters, but it does mean a somewhat reduced sense of security for home owners too. Mind you, this is already the case for any existing property tax or council rates, which exist in many/most places, so it's also kinda a non-issue.