I should not (at least it was never meant). It is not _current_ layout (is the a word "Current" in UI?), it is a  layout which name is displayed on the top of the window.
Redisplaying layout is a massive and slow task - is there real requirement for making it "realtime"?

When I press shift or ctrl, it highlights.  That immediately suggests that if I use ctrl+shift to switch layout, it updates...

Keep it as a feature request then.

It can cache the layout display of course.

Use case: I want to compare key placement between two layouts (e.g. to learn a phonetic layout's correspondence to English letters).  Currently this requires opening a layout view, switching layout, opening another, maximizing both and Alt+Tabbing between them...  This works quite well but it's not discoverable to beginners.  And it requires a little more work.

Use case 2: I want to learn my layouts while typing, so I'll keep a layout view window open [and always on top].  But when I switch layouts the view doesn't update, so now I have to open several of them and switch between them as I change layouts?  Awkward!

And finally, updating the display in real-time would be more consistent with Gnome's "changes are applied immediately" feel.

About performance: the Add Layout dialog shows layout previews in real time as the dropdowns are changed, and it reacts very quickly.  So it shouldn't be such a problem.

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