I really don't like that the Powers That Be have decided to make this change, for many reasons:
1. Changing the default behavior of a thing on the 'net that's been around for so long. Like the article says, I can't wait to see the various and sundry things that are all broken as a result.
2. To set SameSite=None and get back to the old behavior (more on this in a second), you need to do... user agent sniffing, because some browsers (as the sibling comment by swang says) will choke on None and fall back to Strict. Great, so sometimes set SameSite=None, sometimes don't set it or else things will break. eye roll
3. As the article says, SameSite=None is only allowed on Secure cookies, which means you actually can't get back to the old behavior. Now, my company has been telling people for years to stop using HTTP (and customers have to contact support to even get HTTP support enabled). However, there are a few enterprise-y holdouts. In several cases, we've had to go be the bearers of bad news. Albeit, there is an undercurrent of glee in finally forcing them to stop being bad stewards of data (assuming they don't just enterprise-policy it away), but still, from a business perspective it's very frustrating.
So, in sum, it'll break stuff that's not updated (my guess: a lot of stuff), setting SameSite=None requires a user-agent-sniffing hack, and even setting SameSite=None is not a complete solution if you're using HTTP for some reason.
And for what, exactly? This would've been nice in 1995, but it's a bit late now. Though, I guess maybe twenty years from now we can rip out (or stop writing) some anti-CSRF code or something.