I was just curious. I thought I might have missed something.
NATO is about peace, stability, and security—security, of course, being the means for the other two, peace and stability. Amongst the member nations, I think the mere existence of NATO, maintaining that mutual defence but also stability among all of the 28 nations of NATO, is very important.
Is that one of the reasons for increasing the numbers: to increase the space for stability in the world? In that context, I guess Russia would be a potentially important partner.