RC is optional that's for sure. So expiry of RC is immaterial.
The complication is the SS-related changes brought into EEA Regs last November. Especially as they seem to apply retrospectively.
They seem to have de-recognised
Eind and endorsed the need for BC to be a qualified person in UK.
See
http://www.immigrationboards.com/eea-ro ... 19308.html
Under pre-November Regs, yes the applicant will have acquired PR in early 2017 simply by residing in UK.
It remains to be seen how such a case is now treated, with November changes in place.
But dates of RCs are still immaterial.
Yes, spouse of BC may apply to naturalise under section 6(2) of BNA, immediately after becoming settled; those on EU route now need DCPR/PRC too.