Undo / redo when editing text with a button or phone “shake”.
I already have this working just like on desktop PCs: with Hacker’s Keyboard set to full 5-row QWERTY layout I can Ctrl-Z or Ctrl-Y and get the same undo/redo effects on edited text.
Also possible with futo keyboard app but still, it’s a bit an overkill to install a whole new keyboard app just to be able to perform copy cut and paste text. 
Especially considering the importance of privacy and sensible information that goes through it.
The right place to trigger actions on editable text in your currently active text box is still the keyboard, that’s literally what it was invented for.
Not having all the keys and functions of a computer keyboard is just the unfortunate legacy of the old-school thinking that '“mobile version must mean less functionality”, which made sense in the days of 3-4” screens, but not anymore. (I never accepted such primitivism from any phone that expected me to call it ‘smart’, if there was something I could install or configure to change that. Like setting browsers to load the desktop version of websites always.)
A full keyboard is normal, not overkill - it’s these restricted “mobile” keyboards that are the joke today, with so much screen space available. 