If its trimmed and only last xxx blocks are kept (there are no days in bitcoin as the article nicely puts it) then the people who have bitcoins and just hold it before the trimming happened will lose bitcoins or won't be able to spend them.
Every time somebody does a transaction involving bitcoins mined from a long time ago the entire ledger is need it to see the origins of those bitcoins.
Bitcoin is 12 years old now, and it's 320 GB. I could store 2 full copies of it on what's left of my 2TB laptop SSD.
In another 12 years, that is in 2033, it will be 640 GB. I'm pretty sure I'll have more than 2TB in my laptop by then; and I could fit one copy of that future blockchain on my SSD right now.
Or to put it slightly differently, I can fit the whole BTC chain on a $20 USB stick.
Every time somebody does a transaction involving bitcoins mined from a long time ago the entire ledger is need it to see the origins of those bitcoins.