BigBagKbdTrixXKB VS kmonad

DreymaR's Big Bag of XKB tricks implements an Extend layer with XKB (I haven't tried it tho)

Similar features are supported by several applications such as KMonad. Basically the only reason to prefer a firmware solution is if you often switch systems (physical computers, virtualization, remote desktop) and keeping more of your configuration in the keyboard is simpler ... and I suppose if you run into latency issues with features like tap/hold.

A lot of my input customization is better implemented [on Linux] in KMonad and then the usual XKB ... and Emacs (or other text editor).

if somebody is reading this and not familiar with the way how to mod the laptop (or any other) keeb, check KMonad. very slightly buggy but amazingly powerful. and i think there are some alternatives. havent done the proper research though

I’ve used this: https://github.com/david-janssen/kmonad

Extra for hands? I think if you're playing a game where you have enough time to move your hands from wasd or whatever, you'd be able to have time to make more use of the keys on your standard keyboard. e.g. it'd be worth looking into AutoHotKey or https://github.com/david-janssen/kmonad to come up with things to solve your problem.

I use KMonad to make it when I hold the space par the home row turns into number row

e.g. https://github.com/david-janssen/kmonad/blob/master/keymap/tutorial.kbd would be a fancy thing to look into that ought to support most of this without needing to buy a new keyboard.

Remapping the physical keys on your keyboard is not usually something that's in scope for window managers. If you want to do things like that, you can look into setxkbmap and xmodmap for X11-specific solutions or even something like kmonad for something that works in the TTY as well.

kmonad may be a good option.

Kmonad https://github.com/david-janssen/kmonad (powerful software meant to replicate what custom mechanical keyboards can do, but it's not very well known)