I don’t think an annual property/wealth tax is practical although valuing property is not difficult it’s done routinely with probate and when property is sold.
It’s much easier to tax on sale or death when the cash is actually available, older homeowners living in a valuable property just don’t have the cash to pay an annual tax.
If an Property Tax was brought in wouldn't it be possible to allow people over a certain age to have their property tax held in abeyance until the house was sold Katie?
If you raised the age this scheme started at by a year each year, that cohort would gradually disappear. Those younger at the start would know they needed to add this into their calculations when deciding whether they can afford to stay - as many already have to when incomes are lower.