Yes, tab groups, along the topbar, or as most users will jump to "chrome-style"
Now yes, I know that Workspaces are opera's implementation... they're not the same... at all. I've my gripes with the workspaces as is, and how their presentation doesn't match with their function, but that's for another topic.
what: But yeah, simply put, a feature to allow users to group arbitrary tabs together in a nameable group, along the top bar. Where tabs can be easily and rapidly shuffled between groups by the user.
why: How is this different from workspaces? and what purpose does it serve that workspaces can't? For me personally the final straw is when searching for houses and jobs, I've Needed a way to group together places I've contacted. places I've seen/had an interview but still need to send them documents. and places I'm waiting for a final response from. I think you can clearly see how workspaces are wholly unfit for this purpose even at their conceptual level, no amount of fixing their existing flaws will ever make them usable for this. I also think this would actually work very well nested within workspaces, especially since the need for this style of grouping normally arises within a single.. well workspace or task. Aside from that I think given the sheer number of duplicate "where my chrome groups" suggestions/questions, it's clear that it'd help people migrate easier. And as for myself, I'm going to need to reinstall chrome until this is implemented, I just Can't deal with trying to find a house when every time I wake up I've completely forgotten which I've contacted or what.
TL;DR: Top-bar tab-groups are conceptually and fundamentally different from workspaces, tab-groups allow granular/in progress sorting in a way workspaces can't, it'd help users switch to opera and make them stick around, and wouldn't make workspaces any less useful.