Well, Russia being part of NATO and what the consequences are... I guess we'll never know.
What would happen if NATO seriously offered to take both Ukraine and Russia as members TODAY?
NATO would have become a dysfunctional organization. It is not about the Russian fear of NATO. Russian political system cannot get over its loss of an empire, despite us living in the XXI century. It's entirely different root of the problem..
Eastern and Western Europe would have been crazy to gamble everything on the hope that admitting Russia to NATO somehow neutralizes Russia, not NATO.
NATO exists because of Russia/USSR's bad behavior.