I trust the UK's Office for National Statistics will shamelessly borrow the idea of a Time capsule from their counterparts in Central Statistics Office Ireland:
Your Census 2022 household form has a new feature – the Time Capsule. The Time Capsule is a dedicated space at the end of the census form for you to leave a message – if you wish – for your descendants / future generations / historians. Your message can be about anything you want, to anyone you want. Like the rest of your form, it will remain confidential until all of the Census 2022 forms are released to the public in 2122. The Time Capsule is completely voluntary, and it is entirely up to you whether you wish to write anything here or not.