I’m thinking of switching my thumb keys (currently space and enter and two of them go to a symbols layer) to shift. I find that shift makes me anxious when typing because i have to partially leave the home row, and as a result my pinky placement when typing is bad, my ring finger tends to take over and my pinky has become a mod presser and not a typing finger.
I have tried to overload the home row keys as modifiers but that is a huge mistake as it causes misfires or takes TOO LONG to aviate, there is no middle ground with that one.
I’m not using the thumb cluster for shift and other mods, but rather homerow mods. It takes a bit to get used to, but I feel like it is very confortable. I have S/shift and L/shift (tap/hold), so if I need to shift a key from the left hand I use the opposed hand to shift and vice versa. Also pressing both S and L at the same time will toggle caps lock which I find very convenient.
Homerow mods allow me to keep my fingers on/near the homerow and reduce A LOT hand movements.