FYI, the result turns out to be that the old non-EV cert can be used to sign a driver that is used for Win10 after Win10 RTM release. I built Npcap 0.03 r3 today and tested it against Win10 RTM x64, and it installs successfully and runs well. It's a pity that I didn't buy a 3-year cert, but the good new is that I can still use this old one for future releases.
I have found this link: https://www.osr.com/blog/2015/03/18/microsoft-signatures-required-km-drivers-windows-10/, in which it says: "These requirements only apply to Windows 10 and later. In fact, Microsoft plans to offer a bit of a grace period: Drivers signed before Windows 10 RTM will be able to use the older signing mechanisms. But once Windows 10 ships, if you want your driver to run on Windows 10 desktop systems, you’ll need to (a) get an EV certificate, (b) using that signature submit your driver to sysdev to get Microsoft’s signature."
So unfortunately, I think an EV cert has become a necessity for us to sign a driver for Win10 after Win10 RTM release date.
That's quite an old blog entry (March) and from a 3rd party, although OSR are a well respected company in the driver world.