The funny thing is, KDE 3.5.x had the global menu bar as a feature. It didn't get ported to >4.x since there was not much interest.

I guess it still can be done.

How mouse/keys/scrolling behaves, what pointing devices do in what cases are easy cases for KDE. Notification system is also pretty powerful.

The reality is, everything is cross-pollinating from each other. Even if making pixel-perfect copies is not possible, both are pretty interchangeable.

I use both Macs and KDE for more than 15 years now, and can switch from one to other instantly. Both are in front of me during a normal workday, and I just switch without thinking.