Garbage-collected tabs
I tend to keep a lot of tabs open. I mean a lot, like around 200 at the time of this writing. That's spread over 20 windows, with about 10 tabs per window. There's something about the spatial nature of tabs that really works for me, better than bookmarks or other things. Especially because I tend to have a lot of little projects going at once, they work sort of like a project space. You can keep a bunch of associated research together and close it all at once when you're done with it.
But it appears Chrome is not strictly designed for this kind of usage. It tends to get particularly slow with a lot of tabs, both from enormous memory consumption and because websites seem to like to use your CPU for things in the background. I've found The Great Suspender to be helpful for this, though I feel a bit like it shouldn't have to exist. And even without the resource consumption issues, it's still tough to manage all the windows and tabs.
I think an interesting approach would be something like the way garbage collection in programming. What you want is to only keep the windows and tabs around that are still relevant to what you're doing. Each new tab you open would have a reference to the tab you opened it from, and each tab would have a freshness that indicates how interested you are in that tab. Whenever you interact with something it freshens that tab and tabs connected to it. When things get a low enough freshness they are suspended, and if they are left suspended for too long they disappear.
Though unlike with real garbage collection, you'd never actually delete anything. Instead, they would go into some kind of garbage collected tabs and windows history where you could pull them back out if they were needed for something. You could also possibly have some kind of pinning system for things that you want to keep as a long-term reference. Maybe you could even have a nice UI for tabs or windows that are going to disappear, on concertina them if they're stale tabs on a fresh window.
There would be a lot of tuning to do, especially as far as what updates freshness and how that propagates between tabs, but I think it could be an interesting model. The way I use browser tabs (and, judging from The Great Suspender's install numbers, hundreds of thousands of others) isn't in the same iron-clad way that we are used to for desktop windows. It's less like "I need this information to stay here forever" and more like "I'm interested in this now and, in an hour, who knows?"