KDE 4 has a few shortcuts to work with Activities.
Meta+Q opens the Activity switcher widget and shows all activities.
Meta+Tab can be used just like how you using Alt+Tab for windows. To shuffle through all the activites.
Both of these shortcuts don't work in Plasma 5. SystemSettings>Shortcut doesn't have any option for these to be manually configures.
Steps to Reproduce:
1. Press Meta+Q or Meta+Tab or Alt+D, Alt+A
2. See if you activity switcher opens or activities are switched.
Shortcuts don't work
Meta+Q should show all activities.
Meta+Tab should be able to switch to next activity.
Meta+Shift+Tab should be able to switch to previous activity.
Created attachment 89980 [details]
Settings screenshot from KDE 4
These are the settings missing in Plasma 5.
Git commit 037dbf3ca8da09cabfd0c7e60e322153e6cb75e8 by Bhushan Shah.
Committed on 15/12/2014 at 16:15.
Pushed by bshah into branch 'master'.
Register shortcuts for activities management
M +73 -4 shell/shellcorona.cpp
M +4 -0 shell/shellcorona.h