A month and a half ago, Microsoft announced that they would roll back OneDrive storage plans. Subscription OneDrive storage would return to 1TB, down from unlimited. Free OneDrive was hit, too. The service offered 15GB (with a bonus 15GB for using Camera Roll). That was also scheduled to be reduced to 5GB, with no Camera Roll bonus. Users were naturally upset at having their free storage reduced by a factor of 6.
These changes will still take effect in early 2016, but not for everyone. If you are a current user with 15GB base storage, you can opt-in to being grandfathered by clicking a link. You will apparently also retain your 15GB camera roll bonus, if applicable, too. This will not be available for new customers, although there might be still time to sneak in, especially if you have a Hotmail / Microsoft Account / .NET / Passport / Passport Network / Live ID / Microsoft Account (again) / whatever they call it now account. Wouldn't hurt to check what OneDrive offers you today, and try to lock it in.
The Ars Technica article is a bit ambiguous about current Unlimited users. I mean, I guess it won't hurt to try. Be sure to let us know if you're successful. It sounds like it only applies to free tiers, though.
I guess it's nice that Microsoft allows users to be retain their settings. It's interesting that they require opt-in, though. This satisfies the users who are most likely to object, but it directs future users to subscribe. You know, unless they find old news posts on Google.