Subscribed calendars on Windows 10 Mail app?

• Go to http://calendar.live.com and log into your account
• Click “Import” on the top bar then click “Subscribe” on the left
• Paste your iCal feed into “Calendar URL”
• Click “Subscribe” to add the feed

Source: http://dottech.org/190699/how-to-add-ical-feed-to-windows-10-calendar-app-tip/

I have been able to get an ical/webcal in after a few attempts:

All you need to do is add your calendars to your live mail account. Then remove and readd the account from your Windows 10 Calendar, and you will see them in there.

So it is not a direct method, but it works :)