Sometime later this year--no date given yet--the Piccadilly line will shut for upgrades and repairs. It's in preparation for new air-conditioned cars.
I'll update as soon as dates are given.
For many of us, the Piccadilly line is our main conveyance from Heathrow into London. It looks like during the closure only the more expensive options will be available. Or they may come up with some type of temporary plan to overcome this problem.
https://www.timeout.com/london/news/the-piccadilly-line-will-close-later-this-year-041024