Yeah, KIO is an awesome piece of software. Yesterday, a fuse interface was released[1] so that non-KDE software in Plasma also get most of the benefits of KIO.
And speaking of browser tabs, Plasma Browser integration allows to switch to an open tabs from Krunner directly and it works with Firefox, Chrome and Microsoft Edge.
[1]: https://feverfew.home.blog/2020/12/31/kio-fuse-5-0-0-release...
Took a while but it does work, bar a few minor issues. I have problems with certain applications not understanding Dolphin has already authenticated to a share. For example VLC will only open a file if the URI to the share contains the user name required to authenticate (smb://user@fileserver/Video).
[0]: https://bugs.kde.org/enter_bug.cgi?product=kiofuse&component...
AudioCD KIO is still working the same way. I'm ripping an old audio CD of mine to FLAC as I write this comment.
KDE's one of the oldest and best maintained feature is KIO backend. It's still alive and kicking as hard as in 3.5.x days.