If you have an Ergodox or other programmable keyboard or driver you can make a dedicated gaming layer.
Being used to WASD, moving to ESDF with an ergo board is not so bad, but the index finger moves a bit more than with a "normal" board when hitting backwards. A big advantage is the thumb keys
Overall I'd say it's better to game on an ergo board, more keys within reach and... well, it's ergonomic.
I've thought about using the Fn layer in my TECHs for different purposes, either a programming or gaming layer, the problem I see with that is speed. For example, I think the "Lore Master" class in LOTRO is one of the most complex avatars you can play in a game. During battle you have to do the following (with keys) {And hand position on keyboard}
- Move Around [Ctrl] Arrow Keys {Bottom Right}
- Fire buffs [Cmd|Cntrl|Shift] 0-9 {Top R-L row}
- Select Players, NPCs and Self F1-F9 (players and NPCs), Backspace for Foes {Keyboard R-L top plus center}
- Adjust Camera Page Up-Page Down-Begin-End {Bottom Left}
This works very well. The keys are spread across the board evenly, which allows for multiple simultaneous actions, say moving while panning the camera (Bottom Right - Bottom Left arrow blocks), or firing then reselecting while the fire completes (1-5 typically/Left + F1-F6 for player/Left or Backspace/Right + movement for foe).
These could be moved a bit though, say to all home row but then you'd have to break up the sequences (0-9 & F1-F12) to keep the shape of the WASD movement keys. Or you could squash the movement keys, but then you have something really unintuitive. In either case you have something you have to think about that is different from the usual way you type. This will slow you down. Maybe ultimately you'll speed up with practice, and perhaps be a little faster than the regular layout, but I don't think that's worth it.
Keep the default mapping is my belief, that way you are practicing your game play while you work. Otherwise you'll just have a confused mess.