Hi @pawel and @msauer - the plans to build a conversation view / threaded view certainly still exist - and you’ve already found the ticket :-).
There has indeed not been a lot of movement on that ticket aside from some initial research, and that was mainly because other topics have been higher on our priority list, think of features like Grouping by date, filtering for unread items and importing/exporting of emails, calendar items and contacts. Grouping also had some technical overlap (because it alters the mail grid / item list), as will threaded view also do.
In the next weeks we will be looking at threaded/conversation view again and that will bring the ticket ‘back to life’ - but what we already know is that due to the complexity it will take time to implement - right now I do not expect the feature to be available in the next months but I’ll be certain to keep you posted.