It's here - SharePoint 15 Object Model SDK (Technical Preview)
It's time to preview what the next version of SharePoint has in store with the SharePoint 15 Technical Preview Managed Object Model Software Development Kit (https://www.microsoft.com/download/en/details.aspx?id=28768&) now available for download. I have not had time to dig into it, but I'll post here if I find (or read) anything interesting.
Thank you @furuknap for reporting this (https://blog.furuknap.net/sharepoint-2013-sdk-is-out)...