Agreed on the cash flow point, although I don't have much sympathy for people who have come into ownership of expensive properties through inheritance, or obscene capital appreciation over the course of several decades.

As you mention, many people will be able to borrow against the value of the property to pay the taxes.

Unfortunately it is indeed a political problem. What the UK really needs is an enormous, publicly-funded house building programme, but that would of course harm existing homeowners.