Hi ghstryder,
it's not magic, the pager is still there and should be. The bug/discussion you linked escalated a bit, but started from the point that the feature to have different
wallpapers for different virtual desktops was removed, not the pager/desktops itself. If you have one wallpaper for all of your desktops, you won't notice any difference.
I definitely know what you mean about weak understanding of activities. They are not really well documented on official kde resources, and many people do not know how to use them and what for. There are even discussions that the name is misleading and should be changed (
Help to Find Better Metaphors). I myself use desktops and pager, no activities. But several months ago when I wanted to know if they could be useful I googled for articles, howtos and blogposts with searchparameters like "workflow with activities", "productive use of activities" and such. Forgot to bookmark the results, but found some interesting writing about what activities are meant for.
Consider a real life example: your desk in your home office is probably a mess like mine, but you have a certain order for yourself. On the far left the correspondence you are just reading and answering, in the middle a photo album and some glue, on the far right some magazines you read and take notes of. That is your "desktop with three virtual desktops in a row". If you have in the same room near the south wall a workbench with soldering iron and some computer spare parts, and on the north wall brush and easel and some paint, these are a second and a third activity (when office desk is the first), and can have their own virtual desktops.
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edit: found some
http://blog.hanschen.org/2011/02/04/activities-a-change-in-workflow/ http://blog.hanschen.org/2011/05/15/7-ways-to-switch-activities/ http://blog.cornelius-schumacher.de/2015/04/the-space-time-continuum-of-kdes.html https://www.linux.com/learn/tutorials/564826-kde4-activities-for-fast-efficient-workflow http://user-prompt.com/discuss-the-future-of-activities-and-virtual-desktops/