What if I downsize from a $1,000,000 home to a $500,000 home?
With all things being equal your property tax should be cut by 1/2 so instead of paying $4000/year you would now pay $2000/year. Theoretically the costs associated with maintaining a smaller property should also decrease proportionately so continuing to fund your 20-Pay Plan should not be an issue. Then if needed, there are still the proceeds from the sale of your $1,000,000 property that could be factored in to make up the difference.
What if I upsize from a $1,000,000 home and into a $2,000,000 home?
Your property tax in this case will likely double from $4000/year to $8000/year. It would stand to reason then that the financial circumstances that have allowed you to purchase a larger home in the first place, should also afford you the means to cover the relative increase in property taxes. Or if you really wanted you could defer the entire $8000.
What if I decide to sell my $1,000,000 home and rent instead?
Now you will have no more property taxes to pay and therefore no property taxes to defer. Neither will you have any property taxes to repay in the future. ( except for those already deferred ) Continue funding your 20 Pay Plan as before or fund it by using a portion of the proceeds from the sale of your property.