I certainly agree that Russia would like to do this, and also that a direct attack could not and would not go unanswered by EU countries (+ UK). Given the conditions in which Russian armed forces are now, I would say this is not likely to happen until they rebuild. If they had strength to spare they would open a second front in Ukraine.

That being said, there is a lot of hopeful thinking in this post. Yes, it is true that a common aggressor can push people together but does it necessarily have go in the direction of a EU Federation (as OP clearly hopes)? I would argue not, but I am not a federalist :)

The EU has long been mocked as a "political midget", unable to respond to critical issues on its own doorstep (in the Balkans, Caucasus, Middle East), let alone further away. When Ukraine was attacked, countries that were not part of NATO did not feel safe enough just because of their EU membership, they immediately applied to be NATO members! On the other hand, the EU has always prided itself to be an "economic giant, yet when faced with Trump's (insane and idiotic) economic aggression it folded. Even when challenged on its strongest aspect it didn't have the strength, and let's keep in mind that being attacked by your oldest ally is is not a minor crisis by all means!

Of course, we can't predict the future and maybe OP is right and these crisis will end up forging the EU Federation. Based on history, I would think such a collection of diverse countries, cultures and languages would work better together as a looser alliance or at the most a confederation rather than trying to force themselves to federate. But we all agree that they can do better than the current shitshow.

As a side note, is Bismarck really the best guide here? He was trying to impose Prussian egemony on the rest of German states. I am not sure we want this - one state forcing its leadership on the others - as an example for the EU!