There would be hundreds of thousands of DVR systems running on Windows XP globally, if not millions.
Microsoft has pulled a plug on XP, doesn't mean we all run around getting rid of XP based systems. As for security, quite a number of systems rely upon third-party security software tools from companies like Symantec, ESET, McAffee etc. So as long as those security tools are still going to supprt XP, it shouldn't be too much of a problem.
For XP based systems that are purely relying on Microsoft Security Essentials' or without any security software at all, there will be a huge issue for security; this needs to be addressed right away. At the same time, security companies may start planning upgrade of OS or complete systems, with 'XP support end' as an excuse for more sales.