Sevastopol. That's a major upside and one that didn't exist before. And when I say major, I mean it changes things in ways you can't even imagine. I mean I didn't specialize in naval intelligence or battle planning but even I get a stiffy thinking about how powerful it would be for NATO to have Sevastopol; something we thought was impossible during my time. That is enough to get them in no matter what. Afterall, Turkey was admitted and is basically bulletproof due to the Bosphorus, and Crimea is every bit as strategically relevant as that.
I'll give you more though.
Iceland is in NATO. Iceland has no military. Iceland has no military intelligence agency. Iceland has no signals, human, or geospatial intelligence agencies. Iceland has allowed NATO to install 4 radars there as part of IADS, which could essentially be replaced by a single AWACS and offers no real early-warning capabilities. Ukraine in NATO certainly has a bigger upside than Iceland.
In terms of active duty military size in Europe, there's Turkey, France, then Ukraine. They've got more soldiers than Germany and the UK. If weak Russia does want to lash out down the road, they will potentially see Ukraine as a primary target to make up for their "humiliation", which takes pressure off other NATO nations (and means less warheads for striking other NATO nations).
I have repeatedly said that NATO didn't want Ukraine prior to the war. But the war changes the dynamics. Joining NATO is now in their Constitution. Their society rapidly westernized. Their military is now more interoperable with NATO than a handful of other NATO nations. Any pre-existing agreements with Russia (ie the lease of Sevastopol) are null and void. Plus if Russia loses, they'll be so weak it will be irrelevant what Russia thinks in the immediate aftermath, and in the longer term it won't matter. A new strategy will need to be devised, sure. But with air supremacy and a large Black Sea Fleet now that NATO will have a deep sea port there, it's possible the new strategy might even be better. Heck, those battle plans may already exist even. My experience is more than a decade out of date. Having said that NATO's big-picture strategy wasn't OPSEC so I'm not sure why a new one would be so I'd probably have heard if it had changed, but it's still possible.
If Russia wants to "do further incursions" after that, they will be unable to do so without triggering article 5. If Russia loses because the entire game changes. It goes from "we need to defend against a nation far claims to have a top 5 military", to "we should keep this militarily weak nation weak and, if possible, make it militarily weaker."
Also, there are MNNA's as well as prospective NATO nations to consider and what impact it would have on them if Ukraine isn't admitted now. Keeping a country out when you have a reason, even when it's as ridiculous as "your country's name is the same as a region in our country so change it" is one thing. Keeping out a country after a war with your biggest enemy whose butcher's bill is going to be massive isn't going to win any hearts and minds. Even if there was no other value in admitting Ukraine, there is a penalty for keeping them out.
There's also a military strategic reason why you don't want a military you trained and that has a lot of your cutting edge equipment being angry at you and potentially helping your enemies. Not to mention they're practically guaranteed EU membership now.
All of these things, in my opinion, tip the scales so far in Ukraine's favour that NATO will invite them for ascension in the first meeting after peace is signed. And I wouldn't be at all surprised if an emergency meeting is called to hold a vote. Unless, of course, something changes in the meantime. In the aftermath, if Russia loses and there are no other significant developments, we shall see which of us is right.
