Do you count that in today's dollars or in dollars 20 years in the future?
Anyone who is calculating retirements should be accounting for inflation of 2.5-3%. The typical expected real return from the broad stock market is 7-8%
Assuming the stock market accounts for this inflation with augmented returns (it usually does), then using a real rate of return means your calculation of how many of todays dollars you need to retire is a proper calculation.
There's very few things a retiring person will need in the future that aren't going to generally be covered by a smart planner. Healthcare and long term care are the big ones, but anyone who looks into it minimally or has a spouse with a decent job will be covered. Medicare advantage also isn't that much to just buy.
Vacations and luxury items of course could jump in price, but if they do that substantially it just means you need to work a week a month past 60, which isn't a terrible fate either because it gives you something to do a week a month. Vacations and living abroad gets old for people raised in the US.
Beyond healthcare, vacations/luxuries, and I suppose grandchildren I can't see why a normal goal of 5-10 million isn't totally appropriate.
Could you elaborate why you think people will need to potentially double that goal? At a 4.5% withdrawal rate on 5 million you're looking at 225k per year likely in perpetuity. Basic expenses including meals out should only run about 5-10k per month. How much are you planning on spending once your mortgage and kids are not on the ledger?