There is a Surface 3 (not the Pro) but they have switched to an Atom processor and runs x86 Windows not RT
RT is dead and buried. The product Support Lifecycle page is distinctly uncommunicative
https://support.microsoft.com/en-gb/gp/lifecycle-windows-rt-faq
The "as available" can be construed as never, they rarely admit anything negative. If they do nothing i.e. no comparable upgrade they are still within the terms of this statement.
If, as I suspect is the case, they carefully worded any reference to RT out of the Windows 10 program it would not be an automatic entitlement.