@dAKirby: Thank you for the feedback!
Home page of the project has the fair description, so there should be no disappointment. Everything works exactly as described (quote below):
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An ExtraMagic is the long-awaited solution which serves as Control Panel for both Magic Trackpads, puts the drivers
to PC or Boot Camp, and, most importantly, enables 3-finger / 4-finger gestures in Windows 8 / 10, as following:
* 3-finger dragging, 3-finger tap, 3-finger horizontal and vertical swipes.
* 4-finger tap, 4-finger horizontal and vertical swipes.
These ExtraMagic gestures are highly configurable. In fact, now you get more customizations in Windows than in OS X.
Note: 1-finger and 2-finger operations are still handled by a stock Boot Camp driver
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Second question was about the custom keyboards shortcuts or custom actions. This can already be achieved: you can use the well-known "AutoHotkey" tool with ExtraMagic 'Run application..." feature for each 3/4-finger gesture. All you need is assign a file with AutoHotkey script. This really works, you can assign any key combination through AutoHotkey this way. And it's not too cryptic, there are many tutorials on the AutoHotkey topic. Maybe 'compiled AHK script' sounds too professional, but in reality it's simple and is used by a big community of normal users, not developers. This is the already existing way to enhance the ExtraMagic can with any keyboard shortcut for any custom 3/4-finger gesture one can imagine.