The main draw of xmonad is that you can modify pretty much everything, as the config itself is a Haskell file (the entire thing is written in Haskell). There are tonnes of modules to use, you can define your own window layouts and add whatever functions you can dream off - I haven’t seen any other window manager offer this kind of freedom (with the added joy of learning Haskell!).
As for the second point, about half a year ago, they started doing exactly this. Rewriting xmonad for Wayland. Guess I’ll sit this one out.