A nation state's values should align with EU for them to be part of the group. I don't think Russia would ever choose to join the union considering that even UK(which is culturally closer to Europe) left it.
Many Brits immediately regretted voting for leaving after Brexit. They started educating themselves when it was to late and said they would have voted for staying had they known (instead of believing Nigel Farage). The regions that voted for leaving where the rural economically weak ones that even received money from the EU.
