There seems to already be discussion among KDE developers favoring native windows, which is a good sign that this could change in the medium term: Settle on a dialog design (#41) · Issues · Teams / KDE Visual Design Group / Issues · GitLab
However, there are still in my eyes many unresolved problems with Kirigami, which makes me worry a little about the push to convert so much of KDE to it. In particular, the lack of the powerful movable and customizable toolbars from KXmlGui is what I would consider hurts the most. These toolbars are offered by the vast majority of KDE’s QtWidgets applications and I frequently take advantage of their customizability. Other significant omissions include QDockWidget, the keyboard shortcut dialog, KParts and KHamburgerMenu.
I’m cautiously optimistic that Kirigami will in time begin to approach the massive power currently offered by QtWidgets + KDE Frameworks. However, it seems a lot of work will be required to get there. As it stands, Kirigami doesn’t seem to be suitable for the more powerful and complex applications KDE is partly known for, such as Kdenlive, Digikam, Krusader, KDevelop, Kontact, Krita or Calligra. Particularly the latter two, as their interfaces are practically built around QDockWidget.