Microsoft's Group Program Manager for OneDrive, Douglas Pearce, has commented on the relevant UserVoice post:
"For customers of our free service who have over 5 GB of content and who are directly impacted by the storage change, we will offer one free year of Office 365 Personal, which includes 1 TB of storage. These customers will receive an email with redemption information early next year."
"In addition, for our biggest fans who have been loyal advocates for OneDrive, we are adding a new offer that lets you keep your existing 15 GB of free storage when the changes happen next year. If you also have the 15 GB camera roll bonus, you'll be able to keep that as well."
The offer page is here, so go to it.
Microsoft also apologised for the whole mess, saying:
"In November we made a business decision to reduce storage limits for OneDrive. Since then, we’ve heard clearly from our Windows and OneDrive fans about the frustration and disappointment we have caused. We realize the announcement came across as blaming customers for using our product. For this, we are truly sorry and would like to apologize to the community."
The company's aim, especially for professionals and enterprise users, is to have them all on Office 365 anyway - this is almost a no-brainer for such people and comes with 1TB of storage. Which only leaves new users of budget Windows 10 Mobile handsets. Who, hopefully, won't need more than 5GB in the first place? Meanwhile everyone else, the 100 million or so owners of existing Lumias can opt-in and effectively get 30GB free forever.
Comments welcome. Are you all happy now?(!)