I primarily use one thumb key for shift. Unlike pinkie-shift, I can comfortable use the same thumb key for characters typed on either hand.

My layout: https://mark.stosberg.com/markstos-corne-3x5-1-keyboard-layout/

I am currently using thumb shift on all my keyboards as it feels very natural: no need to move the whole hand (unlike classical shift) and no priority conflicts (unlike HRM shift: with HRM, if hold is preferred then you shift letters by mistake, if tap is preferred you end up typing erroneous extra chars instead of shifting).

Actually I combine enter and shift on the same key, giving priority to hold/shift. Since I don’t need to roll enter, there is no conflict.

it causes misfires or takes TOO LONG to aviate, there is no middle ground with that one.

A lot of people use Miryoku to type fast and accurately. There are settings to fix/alleviate this if you are interested in going down that path.

If you are using QMK setting the TAPPING_TERM low (200 or less?) and enabling IGNORE_MOD_TAP_INTERRUPT will help a lot I think.

I’ve been using thumb shift since day one and I don’t see myself changing that.

I use a dactyl manuform with all modifiers on the thumbs. Works great for me.

I tried shift on the thumbs, but didn’t like it.

I am using homerow mod shift. If you are on zmk try urob’s timeless homerow mods:

https://lemmy.world/post/206636

Another alternative to try would be one-shot-shift. Instead of holding the shift key while typing the letter you want to shift, you would tap the shift key once and then tap the key you want to shift.

After that one key press the keyboard goes back to typing unshifted characters.

I haven’t been able to try this, because my keyboard doesn’t have the 6th column with the shift key.

But I’ll try it on my next build.

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.

Did you try bilateral combinations? They reduced accidental misfires to almost zero for me:

https://getreuer.info/posts/keyboards/achordion/index.html

I use a left thumb for shift and prefer it to home row mods.

One of my thumb keys is Shift, and the opposite is Nav (arrows on one hand, mouse on the opposite). Last time I tried home row mods, a couple months ago, I caught up with what somebody said was the settings you really need for home row mods, and the misfiring problem I had before was much improved. But my fingers felt overworked, my thumbs felt underworked, and switching modifier keys when I needed to type a letter key on the other hand was work my brain isn’t used to. For the same reason, I have not put ‘e’ on one of my thumbs as in the Maltron layout: thumbs for mods and space, fingers for letters.

Enter is a key I don’t type nearly as often as space and backspace, so Enter goes on my little finger and the latter two are on my thumbs.

While I’m holding forth, homerow mods are certainly a thing on Colemak-DH (see Miryoku), but I think the better your home row is for typing letters, the worse it is for homerow mods. Letter/mod combos should go on less common letters.

On my Dactyl Manuform I have right thumb managing enter and space and left thumb managing shift and backspace. I also use the option to hold for shift with tap being tab and backspace is Ctrl if held.

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.

Thumb Shift makes a lot of sense to me. Most layouts switch layers using thumb keys. Conceptually, Shift is also a layer. I put it on the same thumb as my Symbol layer key and set up my symbol layer so that it doesn’t need Shift: All shifted symbols have dedicated keys.

Sometimes I need Shift with mouse actions. As I use the mouse right-handed, Shift has to be on the left thumb for that to work.

I tried using shift on my thumb as the hold action for space, but I was not a fan. The problem for me actually things like the end of sentences. I tend to still double space between sentences, so this meant every sentence was tap-tap-hold on the same thumb for space-space-capital. Even worse, I was testing a layout where you did exclamation point with that same thumb by chording the layer button and shift, so such a sentence would have 4 sequential uses of the same thumb!

Now, I actually keep a dedicated pinkie shift key, but the other modifiers are on the thumb. My thumb keys are space (live alone) and all things I rarely roll though (delete, backspace, enter, tab, escape), so on all the ones you don’t roll through, I’ve put the modifiers without any delay: The moment you press them the modifier activates, and then on release it deactivated, then sends the key tap if less than the tap time. This lets you go really fast without misfires.

I use thumb keys with mod-tap (control and shift, combined with some other commonly used keys such as space and enter), so far it works great.

And in case you don’t know, for QMK, there is an option https://github.com/qmk/qmk_firmware/blob/master/docs/tap_hold.md#hold-on-other-key-press that allows faster hold when using mod-tap.

I use one of my mini spacebars for shift, feels 10000 times better than the regular pinky shift keys