Hi,
I had freshly installed from scratch El Capitan on MBP 17" Mid 2010. I went through BootCamp Assistant to configure and install Windows 7 Ultimate 64bit to which I had a key and activated the installation (BootCamp 5.1.5769). I did nothing special other than the steps below.
Once all - absolutely all - recommended and optional updates (other than language packs - I'm using US English) were installed plus the NVIDIA provided reference driver for the graphics (which is identified as NVIDIA 330M), and the system was stable I clicked the Windows 10 upgrade offer from the tray. The pre-install check stated that the Bluetooth wouldn't be supported. I clicked continue and Windows 10 Professional 64 bit installed.
I ran Windows Update a few times after and a few updates were installed. I also reapplied the reference driver. I thought audio was out but after a jump over to You Tube, I can confirm audio works though I don't think the keyboard audio control buttons are functional.
Windows Device Manager shows that there is a problem with Bluetooth. Otherwise, there system seems stable through several reboots and switches back to OS X and then back to Windows. My Windows 10 shows activated and if I want, I should be able to fresh install Win10 via ISO image of the Win10 install DVD at some later time and retain activation status.
I haven't tried to fiddle with the Bluetooth. If anyone can or has more knowledge about the Bluetooth subsystem in these MBPs, I would be interested in learning about it. I can't say there is any possibility of successfully getting Bluetooth to work but I am willing to work at it a little harder. I have has some success on a Lenovo Q150 NetTop all-in-one once (twice, actually as I had to reload the box when I replaced the hard drive) where I managed to fiddle with a Win 7 driver for an Intel Card that was supported on Win 7 but not in Windows Homeserver 2011 (Windows Server 2008 under the covers) and get it to install and work flawlessly. It would be interesting to see what is different for the Bluetooth in Windows 10 compared to Windows 7, 8.0 and 8.1. I'm wondering if the API or something was rewritten or something.