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.
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.