Windows 10 is already here. For sure, not to be deployed at enterprise environments soon, but probably most of us are going to test it from today on.
Nothing from IBM about its support on IBM Notes yet but this answer from Scott Vrusho ?
"Testing is underway with Windows 10 now to ensure a smooth transition. This will help identify if the product will work as is, or if we need to issue code changes for compatibility."
Let's test by ourselves !