I would prefer the following:

I like seeing application icons in taskbar pager, makes more sense than preview images in small sizes.

But great would be seeing previews when hoovering over taskbar pager symbols.

Meens taskbar pager including sevendex. Saves precious space in the taskbar and I don't like the sevendex icon so much.

Second:
I have arranged my 4 desktops in the taskbar pager "peeks" in square. Would be great to have the options to see the number of the desktop on them.

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yup. But a screenshot preview doesn't make sense when it's that small.

Of course. But with SevenDex i must first hover the application button to see what's happening on my desktops instead of just take a look on my right bottom corner of the screen

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that's not what the Taskbar Pager is meant to be.
Have you tried SevenDex?

Much appreciated the new plugin "Taskbar pager". But how about to make desktop "peeks" for the desktop (similar to Dexpot's Desktop switcher) preview instead of applications icons ?